Advice for application
I got through the paper sift last time. I don't know what I wrote that ticked the boxes, but I was thorough in checking that I had answered the questions asked as fully as I could within the word allowance. I also checked and double-checked my grammar and spelling. Note I was mid-late thirties with A levels, plus around 300hours fixed wing time. This includes some very challenging flying requiring precise handling skills, not just PA28 cruising.
For the Compass tests I brushed up on Maths and Physics. I found some sections of the test to be relatively easy, however the one that got me was the hand-eye coordination test. This looks like an aeroplane type scenario, but it isn't. It has one gotcha in that the sense is reversed in one part compared to a conventional display, although this didn't bother me because I fly non-conventional as a matter of course. The main issue for me was that the input / response was also nothing like a real aeroplane, for example when dealing with upsets from a required path, the idea is to put in a small input and return to normal to allow convergence onto required path. This is usually achieved as a sequence of continuous smooth control changes, but the computer test didn't behave as per the model. Here is where I think fewer hours flying experience will be better for you, since you won't have such ingrained, preconceived ideas as to how to handle controls.
So, I failed on part 1 of the school assessment. I did go back at the invite of the school to be assessed for regular entry to their integrated course, and did really well on the rest of the assessment - high scores in the sim (not used for FPP), team exercises and group discussion. Amazingly no major flaws in the psychometric assessment either. The interview was with two BA FOs, who were incredibly professional, polite, funny, and well spoken. If they are an indication of your future colleagues, you are in for good times. I scored top marks for the interview too, and was offered a place on the in-house integrated course.
Unfortunately, finances let me down, so I have gone my own way. I now have a reasonably likely conditional job offer for commercial flying (funnily enough, through a personal recommendation from a former BA Captain). It's low pay, but great experience. I will probably never get to work for BA, which is a shame, but actually I think the loss is mutual and not worth getting upset about on either part.
So, in summary - age doesn't need to matter
- qualifications do need to meet the minimum, but minimum is ok
- lots of flying hours do not give you an advantage on the test
- some flying hours may stand you in good stead on the interview, since you can speak authoritatively about why you like flying
- get your class 1 medical; it's a waste of money to go for assessment including fees and accommodation if you aren't sure you can get the medical
And finally - if you get through, great! It's an incredible opportunity and seize it with both hands
- if you don't get through, can't get it out of your head, and have enough means to try it, think really really hard. If you absolutely must do it, and can do it without incurring huge debt, it might be worth it. But only might, only you can make the decision as to whether it's worth it.