Just expanding on routes a bit.
I left school wanting to be an aeronautical engineer, and got onto a great degree course. En route through that, I spent some time as what I suppose you might call an intern in a flight test department, which really really impressed me, and left me deciding that I wanted to spend my career in the overlap areas between flying and engineering. And I have.
En route, I've done two PPL courses, two CPL courses, two IR courses, an instructors course, a multi-engine course, and most of test pilot school. All but the last I paid for myself. (basically nobody self funds through TPS, it makes an integrated fATPL course look incredibly cheap). I've also done two engineering degrees: a BEng and a PhD, along with an additional university teaching qualification, become a Chartered Aeronautical and Mechanical Engineer, as well as gaining the Eur.Ing. qualification letting me practice as a professional engineer across Europe. Pretty much all of those academic and engineering qualifications were covered my a combination of the state and my various employers.
I've been in continuous flying practice for the last 32 years, I've been unemployed in all that time for less than 4 months, and I've a few things and range of aircraft types in my logbook that the vast majority of professional pilots can only dream of - if not as many flying hours as most of them will have. The only time in all of that I was heavily in debt was after an (in retrospect) very poor decision to buy an aeroplane and lease it to a flying school - where everything went wrong, but I recovered from that.
My point here is that jumping straight into an intensive professional flying course, and then an airline cockpit, is far from the only way to do things in this industry - and from my personal perspective certainly not the best either. Many people have done variations on what I've done - gained professional qualifications that usually lead to more secure and reliable employment, at less initial exposure, and en-route used the professional income to build flying qualifications. Some have chosen simply to have flying as a hobby, some have chosen to jump into full time professional flying when they were able, some - like me - have gone for a more hybrid career. But we do all have two things in common: that we've not gone badly in debt, and we took a few more years to get the professional flying qualifications.
But, realistically, if your son dives in now, he may be employable in a professional cockpit (whilst servicing huge debts) at 21, if he pursues some other professional qualifications and gains the flying qualifications, he'd be thus employable in his mid/late 20s, without the debt, and probably with much valuable life experience as well. It is entirely reasonable also, as I have, to do all of this within the aviation industry. For all of us, we're employable as professional pilots up until at least 65, and the difference between a 38 and 43 year career really isn't that important, I'd argue.
There are more routes than the ones being proposed by those selling expensive training courses!
G