My 2c
For what it's worth I'll put my 2c in. I applied last year via OAA. Very late 20s, private sector professional (management level) mid PPL, degree and relatively (although not recently) academic. I got to the 2nd stage but not to waterside and have decided against applying again this year, largely due to the long timeframe of the process, and uncertainty over when you would start training let alone flying. That is purely for personal reasons though as I now have my PPL and want to start commercial training now and also want to do some FI and light/TP aircraft flying before diving into a shiny jet.
I firmly believe that this is the best option out there for flight training and were circumstances very slightly different would be applying again with gusto. I truly hope that one day I end up flying at BA.
Salary should be very low on your factors to consider. The fact that you will have a job at all in this market, and that you will get back your investment (word chosen deliberately) in your training over 7 years is incomparable to any other schemes. If you want good money and travel go into an international sales job.
My advice for the process if you want it.
1 - read the FPP website....fully, then read it again. If you are asking if xyz grades are ok and the answers are on the website, you will struggle.
2 - take time with your application. Get friends family etc to help you and proof read before you hit submit.
3 - brush up on your maths and physics, particularly if like me it is a while since you last did any. Also try some online aptitude tests, especially if you have no idea what these are. They helped me immeasurably on the 1st day at Oxford.
4 - I think my failure was at the interview phase (as opposed to group task) but I could be wrong. My major failing I think was I simply didn't know enough about the industry. I was interested but hadn't done enough research. Read some magazines, websites other than Pprune, look at BAs corporate website and get as much info as possible starting now.
5 - finally be yourself - hopefully yourself is something they find interesting. They are looking not only for future captains but also need to imagine what it would be like to sit next to you for 12 hours in a small room and have a 4 day layover in a far flung corner of the world with only you (and of course the CC) for company.
Best of luck to everyone who applies. I'll follow here with interest and hope to join you one day.