I'm 42, people don't just turn into a dry sack of bones and skin after they get out of their 20's. I think that's a common misconception about age. I'm actually in better shape, have more energy than I did in my 30's. It takes a little more effort, but not that much more. If you're unhealthy in your 20's-30's, it can catch up to you when you hit your 40's (skin damage comes immediately to mind). But as long as you take care of yourself....yeah, you have a long while for sex to be enjoyable
And guys in their 30-40's tend to have something a lot of guys in their 20's don't: training on holding, ahem "on" until their partner is satisfied. Some guys have it right away but generally that takes time and experience. Women also just know more about their bodies as well, and what guys like too. Its not an age thing, it's an experience thing.
Personally I think that in your 20's is a good time for sexual exploration, safely, of course.
Life is not a sprint, it's a marathon