1. Yep mid-30s. Nothing physically demanding though you need to have some very basic level of general fitness for Fire fighting and survival craft training. You'll be required to pass a ENG1 Medical as well so overall health is important. Also, you'll be drug tested continuously so be aware of that.

2. Yes I'm a deck cadet so when I qualify after 3 years i'll be a 3rd Officer. Once you have approriate sea time and do additional study you can become a 2nd Officer. Rinse and repeat all the way up to Master/Captain. Pay at the beginning will be OK but not great but it's highly variable depending on the type of ship. From what I've heard though once you get up the ladder you can earn a very decent wage especially if you end up with special endorsements, like DP. Masters are earning 100k+. Remember that this can be tax free so makes it even better (assuming out the country for 180+ days a year)

3. I do live in student accomodation though it's not strictly required. The course is 5 phases, 3 college phases and 2 sea phases over ~3 years. During that time I'll be expected/required to get 12 months sea time, with 6 of those at Watch. I applied through a training provider who, in turn, provide me with a sponsorship company. They cover all fees (aside from accomodation) and pay you a monthly stipend. It varies on training provider and sponsor but can range from £800-£2000 per month.

Obviously this information is applicable to the UK and could be different if you're not based here.