I have a 2 year old 15hh quarter horse mare and I was wondering when I can start running barrels. I don't want her joints to be under to much stress at a young age. I have heard 4-5 years old, what do you think???
Most are started at 3, just make sure her knees are locked. But it's not like your going to start "running" for a long time any way. Least you shouldn't. Just cantering the pattern in warm up classes and such. But most people here don't actually run real classes until their horse is 5 so they can possiably do futurities.
I've saddle broken at mid to late 2 year old. (saddle breaking DOES NOT MEAN get on and ride the tar out of em. It means saddle em up and sack em out.)
Turn em out til 3 year old year and start their training under saddle.
A LOT of your timeline is going to depend on the individual. Some horses mature slower than others. Get a vet out and pull some x-rays to make sure the horse can handle their work each step along the way.
Running? Unless you plan to futurity the horse, there's no reason to get in a hurry. You've gotta think... even if the horse was a 6 or 7 year old... that's AT LEAST 10 years of running left. So what's the rush?