See horse teeth and the anatomy section of horse someone got it right in one or the other of those sections, in that they phrased it that the teeth ERUPT continuously thoughout its lifetime, which is more accurate.  If you want to let me know which page has the phrasing "erupt," I can do the wordsmithing.  However, I have never heard of age 12 as when the teeth stop growing, so I am not certain you have it correct either.  I would suggest that someone get a source on this before we mess it up too much.