Age is tough. Young boars start small then get huge then get small looking yet lanky. I have seen what I thought was a very healthy young boar come back with a old tooth report and I have seen bear that looked like they where on their death and commited suicide only to find out it was a three year old bear having a tough time.
Best way for age is the size and look at the hide, the older the boar the worse the hide. Look around the hawks, muzzle, inside/back of the fromt legs or the “armpit” area. If it looks raggy 8 years plus. Round short nose on a boar its is very young. If he looks like an anteater give hime some years.
Best way is to get a tag, harvest and send a tooth…can’t go wrong that way.