Potentially as young as 13, depending on how far back they are going (13 year olds were admitted for officer training up until the late 1950s). More likely 15, 16, and 17 year olds - the Navy was still taking boys at that age until 1986 (and still takes some 17 year olds).
I joined just before my 16th birthday, but experienced nothing like this. I’m horrified. I always felt very well protected from anything like that. More protected than I wanted to be at times (”Here’s your lemonade. No rum for you.”)
Good to know. Been asking around here re: child Navy and nobody had a clue.