I didn't start ridding my Quarb until he was 4, and that was light trail ridding for awhile. Before that he got a lot of ground work so he'd be ready. I am training a coming 4 year old paint Quarb now, i had her since she was 4 months old. Since she was a yearling I have put a pony saddle on her and ponied her while trailing through the woods. This got her use to other horses, water, deer etc..... there is a lot you can do with a baby besides ride. She is filling out now and mentally ready for more training, but it still will be just trail riding for another year.