I love what you've written.  It seems to me like the issue isn't so much about age, per se, but why it is that age matters.  People, in general, want to have sex.  Telling people to wait until they are married AND telling them not to get married young is a painful way to tell them to ignore their nature.  Now, on the other hand, telling people to marry young, with a wink and a nudge at the impending fulfillment of their primal urges is also not right.  People should be getting married for the right reasons; love, partnership, and friendship among them.

Sex isn't talked about openly in our society, and especially not discussed openly in most religious circles.  It shouldn't be a defining characteristic of married/not married.  I think we'd all rather see people having (responsible) sex before (a successful, lasting, loving) marriage than seeing kids jump into marriage just so they can "do the deed" without guilt.