I think one of the main reasons they're trying to attract pilots straight out of school these days is so they can actually get more productive service from them.
I applied to join when I was 16 and was told to apply for the bursary/cadetship scheme as that's what the RAF needed at the time apparently. After 4 years at Uni, 5 months waiting for IOT, 6 months at Cranwell, 4 months holding for BFJT, a year at Linton, another 4 month hold and now with Valley still to come, (no doubt with another bloody hold before 19Sqn!) I'm going to be at least 27 before I'm combat ready. If I get selected as a (spit!) creamie I'll be pushing 30 which only gives me 2 tours to get more bitter and cynical before I can leave with a pension!
Compare that to the guy who comes in at 18 and reaches the front line at age 21/22. I know which one makes better sense to recruit from a financial/productive viewpoint.
Don't get me wrong, I enjoyed my time at Uni and got an extra years seniority out of it, but the RAF seem to be wanting them younger these days.
Hope this helps.