That's a great gig you have with BA - don't develop expensive habits, use the money to do a PPL, start adding licences and ratings as time and money permit, and at some point you'll either be in a position to apply for a professional flying job, or decide you'd rather just do it as a hobby (or, say, weekend flying instructing).
Either is a good answer - but at your age, with a great career opportunity ahead of you, you can afford to take your time.