Having been a long time league/association exec, I can assure you that this is true in women's hockey through all age groups and teams up to the university level. I also just checked-- on my daughter's college team last season, more than 1/2 of the players had birthdays in the 1st four months of the year.
While the late birthday players may in theory catch up as everyone matures by around 14-15, this ignores that fact that all along, they have not faced the same level of competition and challenge to achieve their potential either, since they were not on the top teams in the age group at the younger age levels. They would have been playing all along at the next level down.
Furthermore, in Canada at least, late birthday kids are not a grade behind their teammates. Those born on January 1 through to December 31 are always in the same grade, except in the relatively rare cases where their parents opted on their own to hold the late birthday kids back a year.