The same coming-of-age tradition that in an agrarian society segues naturally into marriage and family can, in a more permissive cultural context, function as a license for sexual activitity and unwed motherhood. The same network of extended families, churches, and stay-at-home mothers that sustains a traditional social order can provide a temporary cushion that makes second-generation family breakdown more socially acceptable than it should be.Which brings me to b'nei mitzvot. Nobody's kidding nobody that a thirteen-year-old boy or a twelve-year-old girl are ready to join the adult Jewish community. In some jurisdictions, they're still not even liable for their own tortious (personal injury causing) conduct. For various reasons, we don't really hear about teen pregnancy in the Jewish community. But that's not the point.
We still have an "out into the world" ritual for people who aren't going out into the world for at least five more years, usually more. Does that make sense?