The conventional (conservative/economic liberal/libertarian) wisdom is that employers are reluctant to hire new youths because these states mandate so many employer provided protections for any new hires. Employers become risk averse, unwilling to give anyone untested a first shot at the labor market. Evidence is somewhat mixed based on this chart. The UK has traditionally had lower severance ("redundancy") pay requi…
Edit: for the record, I'm from Bulgaria and our unemployment rate for under 25 years-olds is 28%, according to latest Eurostat data. Back in 2008 we were at nearly German levels (11% vs 10%). Interestingly, Germany is the only country whose rate has gone down rather than up in the last few years. Their graph is almost perfectly asymmetrical with the ones for countries of Eastern Europe.