This is a unique industry where you have to back a horse early on - rocking up at BA in your mid 40's, in my opinion, is too late.
Well, I left a TC position with a UK 737 operator at the age of 42 and joined BA on the 747. Best career decision I ever made. Don’t misunderstand me: I took a huge pay cut at the time and I fully understand that this was 21 years ago and even then it was not for everyone. I remember one of my colleagues who joined with me and left after about 6 months.
Would I try to talk someone else into doing the same now? Probably not, as their career path will be different. Everyone must assess and make their own decision but I just wanted to point out that it worked for me.