First you need to know you can adopt a horse, because there are a many horses with no owners, and they need a good place to live. There are a many places were you can find a horse. In internet there are websites where you can find information. A horse maybe cif yopu buy it , you can find for only $5,000.00 or less. Also before you buy a horse you need to talk with a veterinarian about the horse, because many people are sale their horse only because they have a injurred
By itself, age is not alway a reliable indicator of training and experience . You want a horse who was been there , done that and very experienced under saddle. There are older horses out there who have been "pasture puffs" and have a little store.
Age vs . Experience
Buy or adop