Ugh, poor girl. I am willing to back and start riding a horse consistently as a long 2 year old if I have to but I prefer to wait until 3 if possible. I know lots of those horses that were started as long yearlings and early 2 year olds for shows and all that. Too bad that at 15 or 16, they are too crippled up with arthritis that they are unusable :(.
And one thing that many people probably don't agree with me about is that I don't spend any days or weeks getting the horse used to the saddle. Most times (providing the horse isn't unmanageable) the first saddling is also the first ride. With proper preparation and good groundwork though I have yet to be bucked off on the first ride. They usually wait until about 2 weeks into training when they are sore before they throw a fit if they ever buck at all. :p