Hi there. Well, quick questions, quick answers!
Would I need to attend a flight school first in the UK, and then work my way into an airline interview? Or can I be hired directly?
Definitely the first one. More than you can possibly imagine. Since I reckon you're American, I can't really write about your potential picture down there. Yet, just to make you aware, it's likely to be tougher than normally expected.
Is 25/26 too old to start?
It's kind of mid-range to begin. But getting an employment really depends on the very minute you walk in, quite regardless of your age. So don't worry about that too much.
Once you get a job with an airline, you are required to stay at your current airline or else you will start at the bottom of another carrier's roster if you happened to move, is this correct?
Not exactly. It's not a fixed and golden rule. It depends on the single airline and -again- the timing of your application. Of course if you're very high in the roster, you can expect to lose some altitude by changing airline. But let's say you finally made it to become a Cpt; then, if another airline is looking for captains, you will likely jump in directly to the left seat... Hope it makes sense.
So, you are not really stuck in one company for life, yes?
I would say: UNFORTUNATELY, you aren't. Again more than you can possibly imagine
Cheers, mate