The real adulthood doesn't look like the teenagers want it to be. They are always confident that adulthood would bring pure freedom and choice, but everything goes right opposite. The number of limitations and responsibility grows with the age. The government controls nearly all your movements, there's nothing you can do without the 'allowance'. So where is that freedom?
Moreover, you always have to spend most of your time at work to keep your head above water, and no one cares if you don't want. No money - no possibility to survive, so it's very common for young adults to shoulder heavy debts. As a result, almost everyone is put under pressure to get ahead in the rat race.
One more disillusionment is that they don't feel they can really make a difference. The leading positions are occupied by elder adults, and they're not going to let the youth step into their shoes. So young adults are forced to get on the carrier ladder little by little, even if they're working for the public good.
Young adults take to the streets to march in protest, create various political meetings, but the government takes no notice of this at all. As a result, the youth becomes alienated from politicians, but not from the issues. Even though they feel that there's no difference who is in power, they're keenly aware that it's their civic duty to vote in the general election. They start volunteer organizations, trying to raise different social problems (like ensuring equal rights for everyone or addressing the causes of global warming), but, unfortunately, it's almost impossible to change something without active support.