That’s actually a pretty good question. I know how to judge the size of a bear walking around (big bears look they have short legs and small ears because their heads and bodies are so big), but after the fact? I guess maybe the size and depth of the paw prints?
I’ve confused bears as black labs before. Bears can range in all sizes. Age is not a definite factor. I’ve seen six year old bears half my size and two year old bears twice my size. The little ones tend to be really smart. The big ones tend to be just big pushy slobs that don’t care about much of anything.