Why do swimmers reach their peak performance at a relatively young age compared with track and field athletes? Particularly female swimmers seem to produce their best results in their late teens to early twenties. This seems to be true for both sprint and longer distances.
By contrast, track sprinters peak at an older age than swimmers, and endurance runners even older. Is there perhaps a buoyancy issue? Do younger swimmers who are not fully developed physically have an advantage because they have built up the muscles they need through training, but have an overall physique that isn't fully bulked out, meaning less dead weight? Compared with track athletes, a streamlined body is more important since water drag is much greater than air. I would be interested in an answer that addressed the physiology involved.
Edit: Here is a study using the career performance of thousands of athletes. http://www.springerlink.com/content/g338206j72233hq5/fulltext.html Statistically, swimmers peak at 21 and runners at 26. That's what the data says, but the study doesn't go deeply into the physiology of why that might be the case. However, swimmers are still peaking a good 5 years before runners.