I've watched a documentary, many years ago. They made an experiment on a young man and old man. Both were not fit at first. They applied the same program and measured the muscle weight increase, and some other things that I don't remember. In the verdict, they said, there is no significant difference between young and old. You can always get fit, if you exercise!
So, I'm waiting to be 80 years old to start to do some sports thing.
Wait, I'm driving a sports car. Does that not count?