Physical performance is more mid 20s and endurance is 30s. Humans are endurance animals so I’d say that’s a better way of determining peak performance. Either way, 17.5 years isn’t a benchmark on any standard. And to respond to your comment about the Olympians being young, the average age is 27. In my opinion, we see younger athletes because they have gone through more and better training at younger ages than older athletes have. There are also more serious athletes in youth nowadays than there were years ago, so the probability of finding a kid who is gifted or more dedicated to a sport is higher.