In individual sports you can shine out or in sports that are predominantly based upon athleticism e.g American Football. However, most sports around the world are team sports and athleticism doesn't really play as big a part as skill does. Don't get me wrong if you have 2 guys with equal skill than athleticism will most likely be the deciding factor. Although, take sports that are globally popular like soccer, rugby, cricket etc. In all of those sports there are all development pathways. If you don't get in the development pathway early it becomes really hard to cement a spot later on in life. If you're a freak like that American ex-track athlete who runs 100 in 10.13 FAT or whatever than you might get an opportunity to play rugby 7s or whatever later on in life based of your potential. Yet 99% of players are never going to have outstanding athleticism like that so they depend on the pathways and the system to get into professional sport. Thus, being born later in a year is going to be a disadvantage in comparison to being born earlier in the year.
Another huge factor that gets neglected in team sports is the players you have around you. If you're surrounded by good players and playing in a winning team you're always going to stand out better than you would playing in a team of less talented players. E.g you're a striker in soccer. You could be a brilliant striker but if you're playing in a bottom team you're not getting as many opportunities to score goals as you would if you were playing in a stronger team.
The Aussies on this forum could also attest to the fact that lately there's been a lot of mature age AFL players getting recruited. Everybody in the public and the commentators all question how these players couldn't possibly have been spotted earlier on. Yet like I just explained it's easy for talented players to go through their sporting life unspotted if they're not in the development system. You can have all the talent scouts in the world but if those talent scouts are only checking out the top teams or players in the top leagues than there's always going to be a few diamonds in the rough that slip through un-noticed until they persevere long enough with their sports to shine and eventually pick up spots in feeder leagues to get noticed.
As far as an untrained 11.4 goes I wouldn't say it would turn heads. If the coaches knew about his brothers and family than they would give him a shot and think he's probably got a lot of untapped potential. But if you went to a track meet and just saw somebody running 11.4 for the first time you're not going to think that they are ever going to run 9.7s one day. In comparison the first time Australia's fastest man Patrick Johnson ever competed he ran 10.49! He went on to run 9.93. Like you've said before some athletes peak when they're 18 others peak when they're 35 it's impossible to tell when somebody is going to be at their best.
Well USA has 300 million people and say 10% of them descend from West African roots. That's still 30 million. The laws of probability favours there being more talent in the USA than Jamaica. Aside from culture, the other factor to consider with USA is that it's not the best environment for track. The southern states like Cali, Florida, and Texas are a production line for elite and world class sprinters. Go up North to places like Chicago, New York, Baltimore etc. you're not going to get the track times because of the conditions- cold, wet and snow. Geographically Jamaica has better weather conditions for track than the majority of the USA does.
Edit- That's what I like about track though. It's objective. Sure you're racing against other people but at the end of the day if you're a recreational athlete than it just comes down to you against the clock.
