"Today, only half of millennials bother to get their driver's licenses by age 18. Car culture, the 20th-century engine of the American Dream, is an old guy's game." - Marc Fisher, The Washington Post, September 2, 2015. Here is the article.
Kids gain their identity through social networks. And they connect with all that through their smartphones. If they have to physically get somewhere, there is public transportation, which has become cool. Yeah, save the planet. Also, through their smartphone they can get a ride with Uber.
In the process of going car-less they are also being financially frugal. The monthly fee for the smartphone is a lot cheaper than the maintenance costs of a car. In a sense, being car-less is the 21st century version of what the bohemians and hippies had represented. Because you don't have to earn a ton of money working for the man, you're free.
That ethos starts in college, which operates as a kind of socialism. All in one package you get some education, food, a roof over your head, health care including psychiatric counseling, campus transportation, and endless entertainment. Post-college the default is there to expect to continue that wonderful life. And, you can if you don't buy into the consumer economy, which includes big-ticket items like cars.
Growing up is not necessary.