Henry, enjoyed reading this post.... A bit over 20yrs ago I was having the same decisions to make!
Lived on a farm, didn't want to be a farmer. I was boat and fishing mad (still am).. Thought of veterinary, even went as far as spending 2 weeks on placement with my dads vet. Decided I was too thick! Choose maths, biology and geography a-levels still unsure of my career path.
Looked at various options, naval arch, marine biology and stumbled across the merchant navy.
Unsure if wanted to go down the deck route or the engineering route so did both- a dual cadet ship.
Would wholly recommend this as a career path- certainly something worth looking at- paid whilst at uni, travel the world, endless diving, fishing and boating opportunities and unbelievable job opportunities at the moment. I have fished and boated all over the world. Yes at times you are away from home for prolonged periods but you have huge career options and time to make decisions once you get a few qualifications under your belt.
Loads of info avail on line, or pm me if you want some more details or contact details of the mntb and other useful organisations.