Miley Cyrus' Kid Sister Noah -- 13-Year-Old Illegal Driver Tools Around Town with Billy Ray

Miley Cyrus' little sister just one-upped Miley in the reckless behavior department by breaking the law -- driving a car around town even though she's only 13-YEARS-OLD!!

Noah Cyrus was spotted behind the wheel of a Fiat 500 Thursday -- with Billy Ray Cyrus in the passenger seat ... a clear violation in California where you must be 15-and-a-half just to get a learner's permit.

Laws be damned ... BRC looked pretty happy with Noah's skills behind the wheel -- smiling as they tooled around a quiet street in their neighborhood of Toluca Lake, CA.

Truth is ... Noah taking the wheel 20-months ahead of sked shouldn't be shocking -- Billy Ray and Tish Cyrus' M.O. is to let their kids act like adults. Remember, Miley bought her own house when she was just 17.

We called Billy Ray to find out what was up with the illegal driving sesh -- but he hasn't gotten back to us. By the way, BRC and Noah can't be ticketed since an officer didn't witness it.