You people do realize that there is a difference between chronological age and sexual age, right? Puberty hits different people at different ages.
It is not uncommon to see two 14-yo boys on the same team, one who has to shave daily and if he decided to drive a car and was spotted by a cop, the cop would not suspect for a second that he wasn't old enough to drive, and the other looks like he could walk into a 5th grade classroom, take a seat, and fit right in. One has a decided advantage, but since they are the same chronological age, they compete directly against one another.
With girls, sometimes puberty is NOT their friend. We've all seen the 9th grade girl who is #1 on the cross country team and goes to the state meet but is the #3 runner as a senior and doesn't go to states. The widening of the hips, breast development, etc., that accompany female puberty sometimes wreaks havoc on their bodies; sometimes it doesn't. Just because a female is a little bit older does not mean she has an advantage due to her age.