This blogger sums up the reasons Gen Y has a harder time reaching the "adult" benchmarks of previous generations:
Boyfriend & I have had many discussions about the fact that New York is a short-term place to live. It's for young singles who like to party. It's for businessmen in their 20s who want to drink and bone and work on Wall Street 14 hours a day. It's for liberal women who have sworn off marriage and kids and simply want to make sweet love to their professions. But as you approach your 30s, you may begin to see New York in a different light. Most people start to see the city as an abusive boyfriend: It treats you like sh*t, steals all your money & wears you down to a little nubbin, but you keep running back because you love it and believe it will change.
More here. When houses in average school districts cost 500K+, it's very, very difficult to think about starting a family. Throw in the fact that money woes are the primary cause of breakups, and we have a perfect recipe for delayed childrearing.