I don't know where you are hunting or what kind of squirrels you have, but with our fox squirrels around here, size is the big indicator. If you don't have experience or more than one to compare, play it safe and assume it is big, especially if it is a male. Those old boars can be chewy as a shoe, so boiling is definitely in order. You can still fry it up if you want, but boil first to tenderize.