That's fairly possible, he could have spent all of his time in the merchant fleet but told he was in the Royal Navy.
Or, here's another theory, he could have lied on his age to enter the RN before the age of 15 and 3 months, that was quite common as well.

Awesome, I'm not the OP, but that's interesting to me as well; I'll see where I can get this book from!

Following this thread, I'm looking for data about the Turkish merchant and military navies in the Black Sea during WW2, so if there's some info in English (or Russian, French, German), I'd be glad to read it!