Hi Mike,
Welcome to the boards. I don't believe there's a difference between what you consider an "assault rifle" and a regular rifle, also referred to as a long gun on the yellow forms (4473's). For the record, the ar15 you're considering is simply a rifle, i.e. a long gun. Here in CA, the requiment for a rifle is to be at least 18 and a clean record. Handguns require you to be 21 and you must first pass a test.
My guess is, it's similar in your neck of the woods.
Remember, you're not buying an "assault rifle" since those, by definition, are fully automatic, bullet spraying, baby killing, shot-from-the-hip, rambo-style weapons that civilians like you and I are too dumb (or not rich enough) to own.
Good choice on the ar15 platform. You'll enjoy it. If you keep hanging out here, though, you'll spend more than your keep on that dang rifle.