A few random points:
- it may be true that peak performance is earlier in life for many sports but unless you're a professional athlete, why is that relevant at all?
- I agree that a lot of people give up early. On the other hand, I've found at 45 that I do need to moderate my activities to keep injuries in check. At one point last year, I was doing boxing, CF, Olympic lifting, and hockey usually 1-3 hours per sport per week, and it was just too much.
- a lot depends on your own body and genetics. Think about those Scandinavian strong men. Not everyone can maintain that level of achievement but in relative terms you can certainly stay in great shape.
- as for an example, when I was in Germany recently, I trained with the World Masters Champ in O lifting for his age/weight. He was 60 years old and 67kg. His face was worn but he had the body of a 40 year old.