Late 20s to early 30s mostly. Some have been trying for years though.
In 2017 it was 26.8. In the kinds of places people on this site usually hail from, it was near 30. (MA being oldest, at 29.3)
Being quite a few years older than when people typically had kids a generation ago, is probably going to result in some differences in how easy it is.
Not saying that's a full explanation either, but it's likely at least part of it.