Marriage and childbearing used to be common in the mid to late teens. Now it's mid to late twenties. You're a bit disingenuous to expect adults to keep the sex genie in the bottle for an additional decade. The "virgins at the alter" is no longer a valid relationship model for many.
But I'm not. I think people are marrying later than they should, and for the wrong reasons. People are marrying later, BTW, in large part because they're not keeping the sex genie in the bottle.