Mark Regnerus, one of the world experts on the sexual behavior of Evangelical Christians, wrote a long article in Christianity Today that states a few important facts.
1. Evangelicals are only slightly more sexually conservative than other Americans: about 80% have premarital sex by his estimate, and other estimates have higher numbers.
2. On average, like most Americans, Evangelicals have increased their average age at first marriage by 5 years, which goes along with a change in the view of marriage. As Regnerus puts it, "Most young Americans no longer think of marriage as a formative institution, but rather as the institution they enter once they think they are fully formed."
3. Women who want to get married have trouble finding men because 60% of evangelical young people are female: 3 women for 2 men.
My addition: recent research from Journal of Evolutionary Psychology indicates that a favorable male:female ratio alone may cause men to dally in making commitment to marriage, as is predictable.
The implications of these facts are not straight-forward because there's little good research on the subject of age of marriage, so conclusions are necessarily speculative. His conclusion is that people should get married earlier. My conclusions are that marriage age among evangelicals will probably stay high until there is an equal gender ratio, but there's unlikely to be an equal gender ratio because across societies women are in general more interested in religion than men, so pronouncements about what should happen aren't useful.
Just stating these facts may help to reframe the abstinence discussion.