Generally speaking I have noticed the demographic make up of congregations tend to reflect the communities they are in. And the communities tend to be a refection of real estate prices, schools, shopping etc. So if the area is one where where young families with kids gravitate there will be young families in the cong. If the area is one where people retire there will be mostly older people. Inner city congregations will have young childless pioneer couples, so forth and so on.
Having said that I do suspect young people and interested people are becoming extinct in congregations everywhere. There's nothing to attract them or keep them. Little ones get to a certian age and drift away.