I would agree that the minimum age of a horse for a first time buyer should be at least 10 years if not older. You want a good seasoned horse. Horses live well into their 30's and are still ridable. Mine is 27 and we lost our 30 yr old last year. Mine is still on the mountain trails and the kids and him are learning barrels together. Get a prepurchase done before you buy. and As far as what sex. Probably a gelding they are less moody. Although my first was a mare and she was a great horse. Just be sure to try whatever horse you are looking at numerous times, to make sure you get along with it and that it passes a soundness exam.