All of my ancestors were here before 1670. In addition, I have Mormon ancestors, which means that I am related to about half the people in the US. Well, I exaggerate a little... but the Mormons were incredibly prolific.
Yes, they were and, by modern standards, still are. I think Utah is still the youngest average age in the country. Partly it is a result of a great red state economy which produces a lot of jobs, especially first career jobs. But even more than that, it is a result of a very fecund population which produces a lot of children.
If we would import a lot more Mormons and fewer illegal aliens, we would get more future and current conservative voters.