Okay, I found this by mistake, so I hope I don't get in trouble for this. You know how if you're rolling a horse on contract, it'll be sent to the Happy Horse Retirement at 33.05 or so? But since it's a contract, when you Cancel/Return the horse, it goes back to the owner. Well...
I was sending over a mass of studs to another account for rolling and one of these such horses (he was 33.05 I think) got sent over since I wasn't paying much attention. Anyway, contract got accepted, he got turned again, went to the Retirement, then back to owner after hitting the Cancel button on the contract. So it would seem if someone had the patience and took advantage, they could roll their horse to some ungodly age.
Thought I should point this out... maybe the horses should STAY in retirement at this point, so nobody takes advantage. Maybe I'm the only one dumb enough to have stumbled across this though.
I hope all that made sense.
*edit* Just fixing my horrible typos.