A study of very young men, 16 - 22, at a health clinic in Philadelphia compared the ones who had fathered children with the ones who had not. None of these guys were married; only a couple (out of 91) were virgins. The average age for first intercourse was about the same - 13 vs. 14. The key difference was that the guys who did not have children had had father figures - 82% vs. 50% - and they themselves had a plan for their lives.
One striking difference between the two groups was how they approached sex. The non-fathers had sex much less often, and were much more likely to use contraceptives when they did. Among the fathers, 70% reported having intercourse more than once a month (the highest frequency category they could choose), and 55% reported that they never used contraceptives. No wonder they had babies. One wonders about the women they had these babies with, since nearly half of the fathers (45%) said up front that they did not expect to support their children.