How long has he been outside the US? That might be more of an issue.
Another thing to consider is that a 16/17 year old whose GC is expiring must have had a GC for several years, long enough for one or both parents to obtain US citizenship. Are you and/or his other parent a US citizen? If yes, he may have automatically become a US citizen (if other conditions of the Child Citizenship Act have been met) and should be applying for a US passport, not a new green card.