I've been saluted a few times by junior enlisted as a 16-17 year old high school bloke whilst touring ships or naval bases in NJROTC. Makes for a surreal situation, but I just return the salute. I have been taught that it is disrespectful to do otherwise.
On cruise, especially youngster cruise, I got saluted like crazy. I think it was khakis + obviously too young to be a chief + crazy insignia = Eh, might as well salute just in case.
It's very awkward. The protocol I was taught was that you return it and, if possible, politely explain that as a mid/cadet you don't rate it.