I think how tired you get might be a better criteria than age. I’m 74 and I just made two 1000 mile drives straight through. That was solo destination driving, though, Phoenix to OK and Ohio back to OK. But the DW switches off with me so no one drives dingy. Towing is very different; I’m a wanderer so I may cover 50 miles or 500 depending on what there is to see. And I’m the sole driver so about 10 hours is all I really care to do which translates to about 500 miles. In practice, though, there’s so much to see in my region I may not move more than 100-200 miles in a day.
