I have two weeks to prepare for a 1 day 10 mile professional guided hiking tour of the Gettysburg Battle fields. I walk a mile a day now easily. But at 74yrs wonder if I can build more endurance in 2-3 weeks for this 2 day tour. First day 10 miles, 2nd day 5 miles over gentle to moderate topography.
In general you can't do that much in two weeks, regardless being 20 or 80 years old. It depends on your general fitness level and your life habits. If you usually are a healthy living (wo)man, being active, eating balanced, no-drinker, no-smoker and so on, it will be easier to get a proper endurance level. On the other side I don't think you can achieve a lot quitting your vices for those 14 days. Like @Chris Mueller commented, quitting the smoking while you are are preparing for the trip could make a huge difference.
If you are somehow fit I see good chances to achieve the hike without major problems. Again, I would recommend the same as for youngsters without regular sport activities while doing your preparations: stay active each day but don't over-exercise. I would make a difference as it is harder to regenerate in higher ages and for example I wouldn't recommend to go jogging. It is quite stressful for the body (joints) and you should avoid getting problems and have to quit your prep-training and also the tour itself.
So I would stick to general (softer) endurance training in the aerobic region like cycling, swimming, stretching and breathing exercises, and of course doing some hikes. The most important is to listen to your body, doing breaks regularly, regenerate and drink a lot.
You can't see this as a benchmark but often oldies are better in endurance sports like running than youngsters, but of course this needs years of training and an active lifestyle. Just had a quick search and found some interesting links, like training past 50 and how to increase stamina.
Most importantly, try not to be overzealous while preparing and also during the tour. In my opinion for sport activities it should be most importantly about the fun!
@user3196 Please give us a feedback how you prepared and if you were able to do the complete tour without major issues!
I'm not 74, but I'm closer to it than to 24. If you can walk for an hour easily, you can probably walk for 10 hours easily. That's basically how humans are built - we can walk the entire time we are awake (unlike our ancient prey, who literally cannot do that.) Some people can't walk for an hour, but I really don't know of people who can walk for 5 hours but not 6. What I would focus on is equipment.
If you have time in the next two weeks, find a one mile route in your life (11 laps of the mall or whatever) and time yourself on it. Just to reassure yourself about the pace. My guess is that a sightseeing trip is conducted almost at an amble, so that everybody can see stuff. It would be very frustrating to always be at the back, constantly arriving to find everyone waiting for you, or worse, to hear the guide just finishing the descriptions. If your natural "out for a walk" pace matches (or exceeds) the pace from point to point in your itinerary, you should be able to keep up no problem.