I'm guessing no one outside the Republican party wonders why young people generally don't vote GOP, but here's a pithy reminder in the form of a headline on Fox News's website:
Fox's resident psychiatry pseudo-expert argues that college first-years have higher self-esteem than ever (except no) while doing worse at school than ever before (also no), which is enough to diagnose narcissism (ha ha no). And it's all the fault of video games and MTV, even though today's young people's parents grew up with those things too. The get-off-my-property crowd hasn't updated their cultural references in a few decades.
So young people are told by conservatives that they need to study harder and be more motivated to succeed today. If they don't, then anything bad that happens to them is entirely their fault and no one should help them. When they actually do study harder and say they're more motivated, conservatives ignore the results and then call young people deluded narcissists.
Not that this entirely accounts for why young people don't like Republicans, but surely if conservatives stopped openly hating The Kids Today they could make some inroads.