Looks like a pretty typical late born 3.5yr or early born 2.5yr old to me. His neck extends down to his brisket but doesn't sag below, nor does his brisket bulge out in front of his shoulders. His front legs are also still longer than his chest is deep. In my experience his chest and legs will be same length at 4.5yrs old, then at 5 and up his front legs will look like stubby pegs on a keg. On the same token, a normal 2.5yr old and younger will have long spindly legs like a big doe. I'd confidently bet on 3.5yrs.
As for score, consider that his eyeballs are 1" diameter, or 3.14" circumference. His face from eyeball to nose tip is 7". And his ear tip to ear tip is 16-17". These measurements are dang near the same on every deer everywhere, regardless if 1.5yrs old or 10.5yrs old, South Texas or Iowa.
He gets 4 girth measurements plus beam length, tine length, and inside spread. Eyes will help you gage circumference. Face will help you gage beam and tine length. Ear tip to ear tip will let you gage inside spread.
However, don't get too hung up on score. Score is not an even playing field. That stud mountain buck right there might just be more rare than an Iowa P&Y buck, and in my opinion is a much better trophy and accomplishment. I've hunted mountains and a buck like that is not behind every other tree. So don't stress numbers is my advice. Go get that sucker on the ground!