Yet again I find myself agreeing with you, those years between 16 and 21 are very important because I think they help shape you. Of course, everyone wants to get out there and have a good time but that has to be balanced against learning to be a responsible young adult. If there was some kind of scheme that allowed non academic post GCSE youngsters to be given the chance to spend 2 years in a varied apprenticeship taster scheme, where they were nominally funded, then there might not be so many dissatisfied youngsters out there. They could experience different trades hands on, maybe for a period of 3 months at a time, with some kind of certification at the end which might then have some bearing on them finding a job in that sector. Alternatively, for the real wasters who just want to get out there and on benefits, there should be required "voluntary" work, like litter picking for example. Personally, I still advocate some kind of 2 year National Service - too many people have completely the wrong attitudes....the "me, me, me" that ORM mentions.
When I look back to how my friends and I were, at 18, we were all working - many of us in the city - and most of us walked into jobs fairly easily, but, we all had pretty decent "O" or "A" levels. If you leave school with nothing now, there really aren't many options. Even if you get good results, it's nowhere near as easy as it used to be.
I admire anyone who can be that focussed, I really wish I knew how I could have got my son to think a bit more like that. He worked hard in his young teens, doing quite difficult paper rounds and extras when called on, as well as helping in the shop and worked hard for 6 weeks full time before being let go as his self employment certification hadn't come through which didn't help. He's had full time work and full time money, you'd have thought he would want that back unfortunately, his peer group aren't the best of role models.