I legit thought pony was a different breed or type of horse, not just a nubbin horseNo no, age has nothing to do with it. Girl/woman is about maturity /age, not height. If a human male is under 5'5" is he a boy all his life and not a man? That's silly. Pony/ horse is strictly about height, not age. Don't muddy the waters! I'm barely 5'1" myself and I became a woman legally on my 18th birthday. Horses also have terminology related to age, such as filly/colt, and it has nothing to do with height.