I have a 7 yr old qrt. horse that is using a saddle that fits him pretty well. This saddle put faded white hairs much like the horse in this video when he was five. Moral of the story don't give up on your existing saddles but certainly try them in a year or two
I have a Canadian Quarter horse that is 16.2 hands high I bought a saddle that might be too small I don't know what size saddle he is and he is a rounded with no withers