According to data analysis released by real estate analyst Zillow, a typical first-timer now rents for six years before buying a home, up from 2.6 years in the early 1970s. The median first-time buyer age is 33 - in the upper range of the millennial generation, which roughly spans ages 18 to 34. A generation ago, the median first-timer was about three years younger.

            There are several factors that affect the decisions of many young adults to buy their own home. The number one reason why they can't leave renting is that they can't save enough money for the down payment of the houses for sale. The median price of first-time buyers who want to buy a home is $140,238, nearly 2.6 times their income. In the early 1970s, the starter home was just 1.7 times the income.

            Another key factor in the longer years of living in rent is the lack of milestones in life. Many young adults choose to set aside marriage and having kids first, to be able to concentrate on their career stability.

            American young adults are "still very interested in buying a house, but they're delaying that decision," said Svenja Gudell, chief economist at Zillow. "Once they start having kids, they begin looking for homes. We're also finding that - given how much rental rates are currently rising - a lot of folks are having a hard time saving for a down payment and qualifying for a mortgage."

            Most of the young adults are just beginners in their chosen career and still depend on their parents' support. Sometimes they can also lean on their parents to help them with the down payment of the homes they want. But this is only an option for those who still have parental support. Many young adults leave their households once they find a steady job and seek independence from their parents.