There are many outside factors that can influence the health and wear of the teeth, and thus make any guesstimate of age just that, a guess. My dad's horse wasn't registered, was a morgan cross of some sort, my godsister had owned him most of his life, then we got him. When he finally colicked and died, the vet looked at his teeth, and said best guesstimate was that he was on the older side of 35+, based on the extreme wear of his teeth, and other factors, but the vet couldn't give us a definitive age. I've had people say that he couldn't be 35, because he wouldn't have any teeth left, they'd be completely worn down, etc etc. So take it with a grain of salt. It will maybe give you a better age range, but it's almost impossible to be 100% sure based on teeth. That being said, my dad's horse at over 35 (I don't doubt he was probably that old), was still jumping really small stuff, but jumping, and barrel racing, and probably would have gone on for another 10 years if he hadn't colicked. He was pitch black when he was born, with just a couple white hairs on his forehead, when he died, he was completely speckled with white, looked almost like he had socks, face was very speckled, and that much grey, took years to occur lol. If you didn't know he was the same horse, you wouldn't think he was. It was amazing. I really wish I had pictures to show.