Depending on his living situation, their teeth can wear faster, making them look older than they really are; from what you have given on his living situation, that could very well be the case.
I have heard of people getting on horses 12 mos (sometimes younger) because they are 'easier to handle'...duh, they are babies, they don't have the muscle tone and strength of an adult horse yet, but to some people that doesn't matter; they are more interested in getting the horse broke, than concerned for his lifelong soundness.
In the area I am living, I see ads like this alot, where the owners say "yearling gelding, mare, colt, NOT been ridden yet." I shake my head everytime, but apparently out here it's common, because I see it alot. And the students I work with, say they break in their babies to ride at a year old; two of them especially keep trying to jump on the 20 mo old QHs we have here, and I have to tell them pretty much everytime, that they aren't theirs, I am the one training them, and they WILL not be ridden until they are well over the age of two. Where I grew up, it didn't seem so prevelant...it was just a given that you didn't get on a horse till he was ATLEAST two years old...I couldn't imagine getting on a yearling.