Yes, maybe in the short term a plumber will earn more. But over the course of a career I doubt it. I also doubt that he'd get the chance to work all over the world & see some of the things I have.
The plumber that I use regularly (on a commercial basis) works 6 days a week, has his 1st appointment at 0700 & the last at 2000. He works all over S London & his travelling time is at his own expense. He pays for his own corgi courses (2 per year) & his own van. He lives in a house that's worth a lot less than mine & my car is a lot nicer.
I'm not trying to do the guy down - just observations that might show that the grass is not as green as it looks.
Pay for aircraft maint. might well not reflect the skill, knowledge & responsibility involved - but there are far worse jobs around. If you're that unhappy where you are now I suggest you move on, I don't hear too many people at our place (or the other similar ones nearby) moaning that they'd be better off as a plumber........
Anyway, back to the 'A' licence. Can't you take/hold it at a younger age & with less experience than a 'B'?
I stand by my comments, take the 1st licence you can hold & take the 1st job you can get. Then plan for the future. I've seen a lot of C.V.s lately & the guys that are in work & using a (A) licence come across a lot better that those with a 'B' & no experience.