RE: How big are the 1.5 old bucks in your area?
I use body size to determine age. A 1.5 year old buck will be the about 120 lbs- the same size as the average doe here.
a 2.5 will be 150 - 160 lb, and noticeably longer.
3.5 Will generally be at least 180 lbs.
Anything after that is unpredictable, but you can bet any buck that weighs 180 or more lbs is going to get taken!