I think there are a couple of factors at work here. The first and most obvious is that young adults are more often engaged in higher education, which effectively delays the point at which they enter the "real world". The second is that it's harder your young adults to earn a wage which can support a family. In my parents and grandparents generation it was possible to leave school aged 15 or 16 and after a few years of apprenticeship be earning a full wage sufficient to start a family without a massive amount of financial struggle. The post WW2 baby boomer generation seem to have had things especially easy in this regard. I think it's only when people begin taking on significant responsibilities - like having children - that they really mature.
Perhaps that's true, and that it's people's perception of what it takes to begin adult life which has changed. Probably there is greater marketing of higher education than ever before.
Many college-age people I know these days are aware that college is just a marketing ploy for most people, but nobody is going to individually risk calling its bluff.
