My paint gelding just turned 2 and he is 15.3, was hoping he would be at least 16.2 but if not that’s fine, his sire is 15.1and his dam is 16.3
Try the string test. Also most horses grow into their 4th year if not longer
I had a 15hh 2 yr old Appendix and he finished just over 16.2!
Star was a bit under 16 hands when I bought him at 33 months. He ended up just under 17 hands. He was not yet gelded when I bought him and I had that done shortly after buying him. He grew the last ~inch from 5 to 6 years old.
I would say that most of ours grew an additional hand after they were 2.
No guarantees obviously but I also use the 2-year old height + 1 hand as an estimate. I think that is a generally reasonable frame of reference on which to base a projection. Most 2-year olds will grow at least inch or two. Some will grow more, some will grow less. But only a few won’t grow at all. It is honestly a total crapshoot. I will say I’ve never seen one shrink!
The general rule of thumb for horses (not ponies) is add 1h to the 24 month height.
You can do both string tests and see how they compare to that additional 1h. The tests are fairly accurate for the horses who are in good proportions. Meaning, they’re likely to be over-estimating the horse who has longer legs relative to his body, and under-estimating the horse with shorter legs relative to his body. And by body I mean vertical height, not length.
I would expect him to get to at least 16.1, probably more. I bought my racing bred QH gelding at 2.5 and he was 16.1. Finished exactly 17H.
All the foals I had out of the mares I bred ( 10 of them ) exceeded or closely matched their tallest parents height.
My current gelding has grown quite a lot the last year and he is 2 1/2+ now. 2 of my last ones really grew between 3-4 years old. They all really filled out between 3-5 years.