Don't remember any age limitations beyond the 18 year olds competing in HS. Being held back for whatever reason stunted several kids at my HS. And, there's a select few helicopter parents that hold back their kids, to allow them to physically develop. My daughter was on the cusp, and Board member asked me, are you going to feel better putting Haley on a plane for college at 17, or at 18. Game over, and we started her in K a year after (had her in Montessori K for that year). Anyway, first thought was to the few, but maybe significant group of youngsters that went into the military straight from HS, and came out with 4 years of eligibility, and college money from the military. Guess they would not be able to compete?