It actually has more to do with the individual pony than you. A well conformed pony, with a nice short back and straight, study long legs will be able to carry you easy. If his legs aren't good the extra strain might do damage over a long period of time.
Also make sure the weight is distributed correctly. The strongest place on their back is between the 9th and 13th vertebrae, anything behind that might hurt him.
Edit: Didn't read that you sold him... so I guess this was pretty useless.
Last edited by Supermane; 07-16-2010 at 02:10 AM.