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.