I commented this on another thread but I will also post it here.
I think the idea is to appeal to voters living in poor areas where the 'yoof' are rough around the edges and spend time drinking on parks, nicking stuff, riding mopeds, smoking weed and generally acting like little degenerates. There is a large group of older people who cannot afford to move away from their areas, and may be long term council tenants who are very afraid of these teenagers. These people may have voted labour in the past owing to more working class backgrounds.
As somebody who grew up in a very impoverished area, on a council estate, I used to hear the old boys suggest things like national service regularly. Along with other far fetched and not particularly plausible ideas around boats and immigrants and anything else that ruffled them the wrong way.
It's one of the stupidest plans I've ever heard and would likely result in being nothing more than a way for them to pass huge government contracts on to their Tory friends and siphon even more money away from places that need it. The amount it would cost to implement and enforce could fund the education children from deprived areas desperately need, but that is too sensible and won't make anybody they know any money.
All round ghastly idea.
I'll also add that there is some structure in place to via community service for people who have committed crimes. If they truly wanted to see improvements surely they could create work placements and service roles for young, repeat offenders, eg under 25s, who lack prospects and qualifications. I don't see how punishing all young people would improve anything for the country. If they decided everybody under the age of 65 had to do it opinions would be very different, but most members of the public has a huge lack of empathy and disregard for anybody who isn't themselves.