Occasionally, someone posts on a forum about being too old to drive a motorhome and full-time or "most-time." Once, someone posted that his 70-year-old mother wanted to sell her house and buy a motorhome and asking if he should be let her!
After deleting the first angry response I had prepared, I posted that this was, frankly, none of his business. (There was more in my final response, although not quite as much as in the original.)
I have met many women (and men) older than 70 in my travels. In fact, I am guessing that might even be a median age for full-timers. I have also met several people who are still driving and traveling alone in their 80s. One memorable woman I met in Zion National Park, told me she was 83 and had driven her 30' Class A from Maine. She had been on the road for 6 months, but had done a lot of RVing in her 60s and 70s. She told me she could not afford to keep her home and full-time in her motorhome, so was thinking of selling her home! Go, Priscilla!!
So, as long as you are fairly healthy, anyone can do this at any age.
And age does not really limit the size of the vehicle you can drive. Newcomers often try to start out with a smaller RV because they think they cannot drive a bigger one. The truth is that if you can drive the front, the rear follows along behind you. Yes, you have to constantly be checking your mirrors so you do not drive over curbs or swing into vehicles next to you. (I have the biggest Class C you can buy, so it has a lot of real estate behind the rear wheels. That means when I turn, the rear end swings about two feet in the opposite direction, which can be a problem in traffic when cars are next to you.)
One of the nicest things about driving a motorhome is that there is no hooking up to a tow vehicle, so it is faster and easier to handle. You also get to sit up REALLY high, even in a Class C, but more so in a Class A, so you can see over most of the cars and trucks in front of you.
Anyway, if you want to motorhome, you can do it, as long as you are fairly healthy and mentally competent. Age in itself really does not matter.