A baseball player's peak age is generally considered to be somewhere between 26 and 29, and during this stretch, it is reasonable to expect a majority of players to perform at the best levels of their careers. This is the point at which they have gained experience and wisdom but have not yet begun to see their physical skills decline, creating the ideal combination of youth and maturity.
That doesn't mean things are always rainbows and lollipops for everyone, though. For Matt Kemp, who has been the subject of plenty of trade rumors this winter, his age-28 season was a combination of extended stays on the disabled list and a fairly miserable performance when he was able to play. Rather than living up to his earlier billing as one of the game's best players, Kemp regressed heavily and now faces questions of whether he can return to his prior glory or if this year was an indication that his body is breaking down prematurely.
There's some good news for Kemp and the Dodgers, however; age-28 regressions are actually pretty common, even for good young players who had established themselves as high-quality players at a young age. In most of the cases, the guys who took a year off from hitting well bounced back to perform at a high level again.