Jocasta. That’s exactly how I feel. For some individuals, mostly older women with kids and a mortgage, I suspect, there is just no way to go back and get yourself back on the correct path when something goes awry. There are too many obstacles in the way. I just try and tell myself that eg I wouldn’t have met my DH if I had had a different life, or yes, I might be much further on in a decent professional role but may be horribly stressed. And keep my fingers crossed that I don’t have to go to any school reunions where everyone would be shocked at how much I’ve underachieved! 
I don’t think schools teach enough about career progression and how to make sure that you don’t end up stuck in an organisation on less than the average wage, with no way to progress upwards and no way to fund a career change or to get an “in” to a different sector.. They don’t advise about the type of organisation which may provide a clear career path. Eg the people I know who have done the most well work for the NHS, have worked their way up from a really very basic position on a shit salary, BECAUSE the training and opportunities are there to progress through the grades.
Even general careers directories, like Occupations, just say things like “once you’ve done a level 3 qualification in X, you could work as a A, B or C, eventually professing to a management role on £x salary.” They don’t tell you HOW to progress from one to the other, ie how easy it is, or whether if you take a particular path you are closing the doors to something else.
Young people are much luckier now, there is SO much information on the internet so they really can find out this kind of thing If they want to. They can see with a few clicks where the job vacancies are, and the job specification that does with it, so you can see immediately EXACTLY what each employer is looking for, in terms of qualifications and experience. Much MUCH harder to do that pre-Internet days when all the information you had to go off was a couple of lines in job advert in a newspaper or the job centre.
Young people can be fully informed these days if they are prepared to put the time in to research.