Wifey did the Catholic Good Friday thing yesterday, and the church was absolutely packed; but she did a head count, and out of well over a thousand people, there were maybe a dozen below age 40.
In my church, it’s the same way, overwhelmingly old people. My wife is the youngest person in our Sunday school class of adults and she’s 60. I suspect that it’s the same in the majority of churches.
I look around in the sanctuary during church and see elderly people with a smattering of children and believe that it’s mostly old people bringing their grand children to church because there just aren’t that many adults there of child bearing age.