According to a recent NCLS report, it was the young who first started to leave the churches in the 1960s and 1970s, and they have not returned. Now, younger generations are absent from the churches in greater numbers.
The larger mainstream denominations are in the worst trouble. You couldn't get a more stark contrast between the Uniting Church (largest age group 70-79 years old) and the combined Pentecostal churches (largest age group 20-29 years old).
The trend is not inevitable. Other denominations (typically more evangelical and/or Pentecostal than the mainline) continue to have very high levels of younger people. The average age of the combined Pentecostal denominations and movements is 39 years of age. Their age profile is actually younger than the wider Australian community.
I wonder why?