For an older guy (say 65+) who likes to hike alone - are a mule or two a help or a hindrance? Maybe a mule for the pack, and a second mule to ride when I get really old?
Historically people preferred to ride a mule - I am not sure it is still practical nowadays :-)
This is called horse packing. It is a totally different outdoor activity to hiking. There are places you cannot go with horses/mules and caring for an animal is a lot of work. Some people love it and horse pack even though they could hike on their own. Other people hate it. Getting into horse packing is a big investment (the animals are not cheap and there is a lot of gear) and it requires a lot of skills. In the western US, you can take guided horse packing trips and see if you like it.
I endorse what @James Jenkins and @StongBad said about being unable to manage and take care of a mule if you are too out of shape to hike alone. I upvoted their answers and your question.
Many trails are serviced by a packer, and you can hire the packer to haul in your stuff on a mule and also haul you in on mule or horse, and then haul your stuff and you out at a predetermined time. This is much, much, much less effort than handling the mules yourself, and probably less expensive than owning your own mules.
As we got older, my husband and I resorted to packers more (although not exclusively). The packer would haul our stuff to our chosen "base camp", we would hike in, and then we would go on from there (without equines).
With this strategy, we avoided carrying the packs on the steepest, longest day of the trip, gained some acclimatization without the burden of packs, and could get to a point where there was ample running water. (Sierras, Rockies.) We did not regress to the point where we had to be hauled in ourselves; at that point, I know that we would have been utterly incapable of managing all the tasks attendant on two mules.
Caveat: If you are experienced with horses and mules, the answer could be different, but it doesn't sound as though you are. And if you are taking a long trip (say, as an estimate, 50 miles or more), the answer could be different.
So my advice is:
(1) See your doc for a complete physical and get advice on how to get in much better shape, and stay in shape.
(2) Get a highly recommended personal trainer and religiously do the exercises your doc and PT recommend. The upkeep of a personal trainer (PT) until you learn how to do the exercises properly is less than the indefinite upkeep of a mule. Return to the PT at intervals to make sure your form is remaining correct.
(3) Go on several mule packing trips with a packer -- a packer who will teach you the essentials of mule packing. You may change your mind after wrangling a mule yourself.
(4) Consider a llama. See this question and answer
Finally, 65 or 70 is not really old, if you are in good health. You can, with religious effort, take years off your effective "hiking age", provided you do not have underlying health issues.
If you are too old and out of shape to hike alone, you are too old and out of shape to take care of a mule or two alone. Animal care is a 24/7/365 job, hiking is a hobby that occurs when you are in the mood and the weather meets your fancy.
Unless you are already hiking on trails, that allow equines (It should be obvious see: Why aren't the mule trains outfitters required to clean up after their animals? ) than the trails you use now, probably do not allow them.
Even where equines are allowed, many areas require special diets prior to bringing the horse to the park. Which either drastically increase the care and handling overhead, or it derails any impulsive outings
Very first thing about mules, is that they eat baled hay for a good part of the year, the lightest bales are around 40 pounds (18KG). Second is that they can be stubborn, the phrase "stubborn as a mule" exists for a reason. If you are to frail to walk with a day pack, you are to frail to manage a mule.
If you really want to consider a pack animal, see the list at What is the feed/day limit for various pack animals? there are several smaller animals that are easier to care for. But this is still a 24/7/365 commitment, if you don't currently have pets, you probably want to consider this deeply before moving forward.
It is perfectly possible to ride mules. They're much the same size as horses, and there are people who do ride them. (A search for "riding mules" returns ~31 million hits.) Some even prefer them to horses.
As a pack animal, you're perhaps confusing them with burros, the iconic pack animal of the Old West prospector. They're a much smaller animal than a mule.
The problems with any pack animal, be it horse, mule, burro, or llama (which seem to be rather popular) start with maintaining the animal(s) when you're not using them to hike (or ride). They need a place to live, so either you pay to board them, or you buy a place with several acres of land and build stalls & barns to store feed & tack. Then they need to be fed every day (usually twice a day), and - if you'll excuse the pun - they tend to eat like horses. They'll need hoof care (trimming & shoeing) and good farriers don't work cheap, and vet visits for shots &c even if they're healthy. And if they're not, well, an emergency vet bill can easily run to 5 figures. (Believe me, I know :-()
Then to get to trails, you'll need transportation. For horses & mules, that means a "full sized" pickup or SUV and horse trailer, neither of which come all that cheap. Then the truck & trailer combo seriously limits the number of places you can go. You just can't get in (and out) of a lot of places, or park at many of the ones you could get to.
When you do get somewhere, you have the work of tacking up the animals, and leading them with you on foot. Because you really do need to keep them on a lead rope. While I don't have personal experience of mules, horses can (depending on their personality) easily spook at unexpected things like dirt bikes and charging bears (again, personal experience). If you're not carefull how you hold the lead rope, this will at best give you nasty rope burns. If you're lucky, the horse will eventually return (more likely if you have more than one, as they're herd animals and like each other's company). If you're not, you're standing there with all your supplies on the runaway critter.
Riding & camping with horses (and I expect with mules) can be a lot of fun, but it can be expensive, a lot of work, and mose importantly, it's something that I would advise anyone but an expert not to do alone.
Horses, mules, donkeys (burros), llamas and alpacas are widely used as pack animals. They would definitely be a help for an extended trek in the wilderness, provided you are capable of managing the animal.
Any animal can be temperamental, but the larger the animal, the greater the risk, both to you and the animal. I've watched a horse buck up on it's hind legs, throw an inexperienced rider and fall back on it's own tail, breaking it's own back - absolutely devastating. I've also seen a rider's face fractured by a horse that decided to jump a stream when the rider was leaning forward. For those reasons, at the risk of upsetting the horse-loving community, I'm personally not too fond of horses as pack animals, especially for inexperienced riders.
Donkeys (and to some extent mules) don't tend to gallop, so they are a smoother ride and donkeys can carry the the heaviest load for the size of the animal.
Alpacas and llamas are generally too small to ride, but can be great hiking companions. They can usually carry anywhere from 30-100 pounds, maybe more, depending on the animal and are generally the most docile (until one decides to spit at you!) They are also known to let out an alarm, sort of an odd shriek. I knew one guy who kept several llamas to protect his goats from bears. The bears don't like the sound and it generally runs them off, so that would also be a benefit for a hiker.
If you are unfamiliar with large domesticated pack animals, I would suggest you start by hiring a guide, or use a guided service. It would be a great way to try it out, and have someone there that is skilled in handling the animal(s). You could even go from a guided trek to a drop trek as you become more familiar before deciding whether you want to invest in your own animal(s).
The cost of purchasing and maintaining a pack animal can vary widely, but if you are using them at least a few times per year, they are more cost effective than ATVs and can go many places motorized vehicles are prohibited.
Good luck!
From your question I cannot figure out on what terrain, what climate, what continent you wish to hike on :) but this read might be an interesting one for you.
There is a guy from Hungary who travels with his donkey, mainly on the El Camino route, but also all around Europe. Here is his facebook page (also with English stuff, but pictures can be useful too) and his blog (with some English stuff as well). I've been following him for a while, he is not hiking on rough terrain. But from what I've seen the hardest part is not dealing with the animal but with humans: he talks about encountering people on the road who take the animal welfare question too seriously, report him to the police because he makes the donkey carry bags etc.
During my hikes in the Făgăraș mountains in Romania I met a cabin keeper who carried up food to the refuge house with eight donkeys. They were all well packed with all sort of food, mainly cans. The donkeys handled the load and the terrain very well, it was steep, part of it in forest, the rest on rocks, but sometimes they wanted to wander away, and the guy had to be really assertive to keep them on track.
I think your idea is great, and you should carry on with it. If I were you, I would consider these things:
Some answers suggest picking a llama instead. I am not familiar with llamas, but I would by all means choose the animal which is local to my area.
