While I am definitely no expert on the subject, I can tell you if you have seen more than a couple you know the difference between a real "hawg" and a young bear. A young one, say up to 150 pounder looks slim at a quick glance. A bear somewhat over that appears to be "a normal bear" 300 lb up appears "rotund". The ears are the first thing I notice on a large bear. They appear very small in proportion to the bears head on a large one. Seems like not alot to go on, but look at pictures of bear where the size is given. You will see what I mean. When you see big'uns in person you know it! As far as judging for book status, I don't have the experience to tell a good bear from a contender but from the bears Ive had experience with, theres no mistaking for a young bear or smaller sow, I do know of some pretty good size older sows taken though. Usually if you have the benefit of scrutinizing, the older boars have a wider head with wide set small appearing eyes. However, its head actually appears quite small in relation to its body size. A young one appears to be skinny with a big head (long) with large ears.