The truth is that there are some things better experienced in younger years. I can't imagine backpacking across Europe is better in your 50's than it would be in your 20's, and if you're doing something with a chance of injury, you bounce back a lot faster the younger you are.
But I really think you're underestimating how active even the average 70 year old retiree can be.
But I really think you're underestimating how active even the average 70 year old retiree can be.