You can take classes in CA starting at usually 15 or 16, but you can't sit for the test and CERTIFY until 18. So, really, I'd avoid them.

You can do damage with both nasal and oral airways. Nasal airways have more complications (bleeding, trauma to the mucosa, perforating into the brain in cases of head trauma), but orals have problems too (usually due to using too large and blocking off the airway).

Anyway, for your BSA kit, I'd avoid them. The chance of you using them is slim, and you're not certified anyway. Not to mention that most likely, either your CPR will soon be taken over by EMS, or you're so far out that you'll have to stop sooner or later.