The NAR says that the first-time-buyer share of home sales has typically hovered around 40% since 1981.

The headwinds facing young buyers are well known: higher student debt, rising rents and a weaker job market have made it harder for would-be buyers to save for a down payment and qualify for a mortgage, particularly in a lending environment where banks are much less willing to overlook credit blemishes or spotty incomes.

Separate surveys, including one by the New York Fed earlier this year, showed that  insufficient savings or incomes were the biggest headwinds keeping renters from buying homes. Many households may also be less able to get help from their parents than in the past, because their parents' homes have fallen sharply in value.

Advocates of looser lending standards may point to the NAR's latest survey to highlight problems on the mortgage market. But it's worth noting that the share of first-time buyers didn't increase during the housing bubble, when it was too easy to get a mortgage. That's because home prices were rising. The share of first-time buyers fell to 36% in 2006, at the peak of the bubble, from 40% in the prior three years.