Gym on Princess cruise?

Question

Hi I'm going on the Crown Princess this March for spring break. I'm 15 and I was wondering if I am allowed to go to the gym by myself. I know on Carnival you had to be 16 to go alone. Anyways, do they really check? I like to work out I'm not an annoying 15 year old and I also look old for my age some say.

Honestly I'm not too worried about it I am just really bored right now and I'm thinking about spring break!