It is not unreasonable to see an Academically gifted and talented student born in 2000 who skipped a grade. The chance of that same child being a gifted lacrosse player may be small, but is not unreasonable.
Where I live the cutoff is Oct 1 1999. There are definitely October boys who should be in 2018 that are already in 2017. There is an August 1999 boy who started school late, not for red shirting purposes, who is in 2018.