At 5 many of mine are just starting undersaddle. Frankly, I no longer believe in starting horses under that age... I used to do it, because everyone did... As years go by I have realized that if I wait until around 5 the horses are just plain more physically capable and mentally ready, training progresses faster for me and is happier all around.
Personally, I won't buy a horse under 5 who is "well broke". Different strokes for different folks.
AlexisChristina... I am 5'8... I still say this mare looks under 15hh. It might be an illusion, but this mare looks roughly the same height against her owner as my large ponies look against me. Again, absolutely nothing wrong with a pony... Good ponies are great mounts, even for adults (even at my height, I am totally at home on a big bodied 14-14.2hh pony)
Honestly... I don't think I'd pay $1500 for this mare. Probably not more than $800, to be totally truthful, and that totally dependant on her having a sweet, quiet nature.