serious question for those answering "yes, immoral" from a Judeo-Christian standpoint. how should we take into account the fact that in Biblical times lifespans were much shorter and people married in their early to mid teens, vs the reality now? certainly it is much more reasonable to ask celibacy before marriage if that marriage happens as the sex drive materializes vs 10-15 years thereafter.
The lifespan thing doesn't seem to be much of an issue. How many people get divorced in their 70's?
As for the difference in marital ages, the conservative reformed types in my community take a number of steps to reduce pre-marital sex.
First, we encourage younger marriages. Girls are usually married off in their late teens and early twenties to guys who have stable jobs. Boys are steered into training that leads to careers. Two year programs are very popular. Second, children don't go away for post-secondary training, and are given a much shorter leash than their secular teenage counterparts with the opposite sex so there's less opportunity for pre-marital relations.
This drastically cuts down on the average age of marriage, reducing the number of decade long waits. I'm getting married next summer; I'll be 21 and my wife will be 19. This is pretty common for my community.
I agree with your general concern. The lifestyles of most people are adapted for a world where pre-marital sex is ok. That some Evangelicals and Catholics encourage abstinence without changing other aspects of their lives to accommodate is is asinine.