My advice is to save your money. In the early years of your naval career the opportunity to arrange regular lessons in advance is very slim. Plus finding the time to do any kind of practicing you're newly learnt skills are virtually zero. I was old enough to drive when I joined but it took a further 4 years before I found time to catch up with what I had learnt before joining and passing my test. Back then there was no questionnaire or hazard observation tests to negotiate either.
Depending on his trade, the navy may send him away on a intensive driving course for free. These are (depending if you work for the navy or are attached to a Marines unit) at HMNB Portsmouth, RNAS Culdrose near Penzance or DST Leconfield near Hull.