Now - clergy perspective (sheesh, this is long and maybe a little bitter).  Almost all of the couples I have married are in their mid 20's - late 30's.  They are often couples whom other churches in my area won't marry, because they live together, they have kids out of wedlock, they are in second or third marriages. So while it is unspoken, that pressure to marry early, to have a "pure" marriage, is definately out there. 

As I was talking with other pastors recently, I expressed my frustration over the fact that these couples aren't allowed to get married other places because they were "living in sin."  Wasn't the refusal of the pastor to untie them only perpetuating the "problem." 

I in some ways prefer to marry these couples. I find that because of all of the stuff that has gone before, it is so much easier to talk seriously and deeply about why this commitment, this covenant, this marriage is important. When I ask them, "why?" they have honest answers.  

That's not to say that young couples don't.  That's not to say that the promises they make won't themselves hold a couple together through all of the changes that will come their way. 

 I think the church tends to encourage early marriage for a number of reasons.  
1) it represents a blind leap of faith and commitment, just like much of our Christian journey. We don't know what we are getting ourselves into, and that's kind of the beauty of it. (as a pastor said recently at the marriage of a friend - if we knew what marriage was all about, we wouldn't do it)  
2)because the church doesn't want to talk about sex in a real way.  It doesn't want to admit that there are healthy sexual relationships outside of marriage. It doesn't want to admit that there is marital rape and sexual unsatisfaction and adultery in marriage. You mention in the article that sex is black and white, either you're having it or your not, but it is far from that simple.  What about masturbation, what about petting and oral sex, what about fantasy, what about role play?  The church wants to keep it black and white - good/bad, yes/no, in marriage/not out of it it  - but it is actually such a complex issue that we don't even know where to begin (society doesn't really either, btw)
3) marriage is the center of the culture war. gay marriage/divorce/children out of wedlock/single parents... I have no idea how this has happened but each of these are seen as threats to the foundations of Christianity. I absolutely disagree and I think that if we really looked at a "biblical" understanding of marriage - we would be far from impressed.  Property exchange, rape leading to marriage, multiple wifes/concubines, inequal gender views, male head and silent submissive female...  (alright, i'm focusing on some of the negative images... forgive me for a minute.)

Yet the church has created its own narrative of a loving and doting young couple who save themselves from temptation for one another and live happily ever after and the church has put all of its faith in that narrative as what will save it from impending doom.