When I got Skip he was just shy of his 2nd birthday (going by Jan 1 as the day he became a 2 yr old). He is and was a nice, solid, big boned horse and looked much more mature than he was. I let him out in pasture to play with the other yearling on the place and they spent that fall and winter just being boys. Come spring I did ground work with both horses. One, Skip, was mentally ready for working, the other not so much. LOL! Harley was and is a CLOWN but slower to get it.
Come Aug. we backed Skippy but not Harley. We did WT, whoa and back up. I took him to a show in Sept for the fun of it, took him in 2 WT classes and brought him home. We had a great weekend and lots of fun. He had the rest of fall, winter and now summer off from being ridden. He'll go back once the weather breaks and it's not so beastly hot and humid. The trainer is shorter than I am, I'm 5'3", and weighs in at 145 lbs. Skip will get worked through fall, get some time off for the worst part of winter, and then back at it again in the spring. We'll hit the show trail next spring pretty hard.
So.....technically he was started as a 2 year old. I don't have a problem with it if it's done slowly and carefully. Even starting him as a 2 year old, he won't be ridden strenuously before he's 4. As a QH stallion, that is VERY late and will cost me in the breeding shed. He'll remain sound and happy though, and that's my focus.