During WW2 the British raised the age of when a boy could go to sea, from 14 to 15 years of age, owing to the high losses of ships' crews. Doubtful if it made any difference, if a 13 year old boy wanted to go to sea, he could lie about his age, plus if he done a, 'Pier Head Jump', meaning got on when the ship was in the locks. Because of 30 foot tides in the Bristol channel in the UK, ships docking there needed to go through the locks before entering or leaving the channel. During that time in Europe, most children left school at 14 years of age, unless seeking higher education, if that was the case they would have to sit an examination in Britain to qualify, if they failed, they could continue with their education, but had to pay for it.
Compared to service personnel, seamen received high rates of pay, and being civilians, plus most ports had, 'Mission to Seaman', facilities, canteen and beds, only allowed to serving seamen. The beef seamen had was not being recognized for their service during the war, medals etc. I believe that has been rectified by some countries.