I tried it as a cadet officer (apprenticeship) when I was 18. This was with P&O cruises. It wasn’t for me, got a bit bored and didnt like thatafter work I generally had to go to to drinks with passengers etc, really I just wanted to hang out with mates etc. (Saying thatthe christmas cruise was great, loads of college/uni girls on holiday with there parents).
Generally only officers were allowed in passenger areas when not working, so dont think you will have all the luxury of a cruise avaliable. Probably a small gym, maybe some deck space, and a mess. All this probably depends on the company and ship.
It is very cheap living on board, you pay for drinks in the mess but thats basically just cost price, only thing else was occasional (very) trip a shore.
Also will you have to pay tax on that income?
Guess my situation was different, I was entering into a career not just a short time on board to save money