At what age would you stop doing just-for-fun agility?

Assuming the dog is fit, healthy and happy to still be running around like a loon, when would you stop them joining in with agility?

I ask because my dog is 12. She's got a lot of energy and really enjoys training. I do little bits of agility-type-stuff on walks with her (jumping over logs, following my hand, walking along things, etc) which she really enjoys. I already go to an agility group, just as a volunteer, and was thinking about taking her along to have a bit of a play during the little dogs session (so the jumps aren't too high) but I would really appreciate opinions. Please do be honest if you think it's an awful idea, I don't want to break her!

Thanks!

Your dog will tell you what she is capable of, my elder dog will be 12 next week and she still does the odd demo (on low jumps)

Parker is 10 and Izzy is 9 and a half and they both still do agility but Parker jumps low heights only. I think you will know when the time is right to stop.

My collie retired completely at 13.5 after doing veteran courses (medium height jumps) for a couple of years - she told me when she really couldn't do it any more.