Join Date: May 2009
Location: Winnipeg, Manitoba, Canada
I wouldn't be looking at her age, I'd be looking at her condition. Her age means nothing if she's still a completely healthy and fit horse with no problems, which it very much looks like. If she hasn't yet had an instance of difficulty with weight loss or any other numerous age related issues, then her body should be capable of carrying a foal. Her fertility will also determine this - the body has a way of decreasing fertility as the body ages and becomes unable to support another life source.
As a maiden mare, I'd say definitely not, but in your shoes, I really don't see a problem. She's foaled before without complications, and she's obviously in extremely prime and healthy condition. There are always risks with breeding mares, I don't personally think you're increasing the risk that dramatically due to her age.
I don't think you can give her a limit - as long as she remains in such fine condition, and easily doing the work you're giving her, I doubt you'll see complications due to age other then the possibility of her being infertile already. Just keep in mind that she is older, and a year is a long time to carry a foal and more then enough time for her to start showing her age more and feeling it's effects. I would say if you're serious about breeding, it's something you likely want to get on top of very soon.
I hope God tells her to smash her computer with a sledgehammer.