[jack2312]

Yeah, there are studies that have been done on this. It's called the 'relative age effect'. It can have an effect into adulthood as well, when a one-year age difference may be less significant. This is because in their earlier years, the children who are a half-year older and more developed will generally see more success, thus getting more opportunities to play, thus getting more practice and coaching, thus leading to more success, etc...

(For more info, see this article [0]. Interestingly from that article, and I didn't know this before today, younger athletes in their cohort who make it to the later stages of their sport are more likely to be "super elite" athletes, probably because they were able to overcome the challenges of playing with bigger athletes in their childhood years.)

[0]: https://fivethirtyeight.com/features/why-athletes-birthdays-...