The average age of people in England and Wales identifying as Christian is now above 50, while a majority of most young adults say they have no religion, the 2021 census shows.
Nearly three in 10 who identify as Christian are 65 and over – up from just over two in 10 a decade ago.
An ageing population and differences in the way people choose to self-identify were among the factors driving the trend, experts said.
The median age – or exact midpoint – of people identifying as Christian was 51 at the 2021 census, up from 45 in 2011, according to new analysis from the Office for National Statistics (ONS).
The youngest average age is 27 years, for people identifying as Muslim, up from 25 in 2011.
Most of the other main groups have seen an increase, with Hindu up from 32 years to 37 years, Sikh from 32 to 37 and Buddhist from 37 to 43, while the average age of people identifying as Jewish is unchanged at 41 years.
The figures show a growing proportion of people in England and Wales who identify as Christian are aged 65 and over, up from just over two in 10 (22.3%) in 2011 to nearly three in 10 (29.0%) in 2021.
At the same time, the proportion of those identifying as Christian who are aged 21-25 has fallen from 5.1% to 3.9%.
The average age of people saying they have no religion has increased from 30 to 32.
Only 8.8% of those who said they had no religion were aged 65 and over, compared with 18.6% of the overall population who belong in this age group.
Census data published last year showed less than half the population of England and Wales identified as Christian in 2021, the first time the proportion has dropped below 50%.
“Many factors can cause changes in the size of religious groups, including changing age structure, people relocating for work or education, and differences in the way individuals chose to self-identify (or how children’s religious affiliation was reported) between censuses,” the ONS said.
Humanists UK, which ran a campaign ahead of the two most recent censuses encouraging non-religious people to tick the form’s “no religion” box, said the latest figures “underline the archaic place that collective worship and faith-based discrimination have in our schools”.
Chief executive Andrew Copson said: “They make plain that the UK faces a non-religious future. This is in stark contrast to how our state institutions operate today. No other European country has such a religious set-up as we do in terms of law and public policy, while at the same time having such a non-religious population.
“Politicians should look at today’s results and recognise they must renegotiate the place of religion or belief in today’s society.”
Among single-age groups, the highest proportion in England with no religion is 52.3%, for both 26 and 27-year-olds, but in Wales – excluding the very young – the figure is 66.0%, for 27-year-olds.
At every age in Wales up to 45 years, more than half of people say they have no religion.
In England this is true only of people from age 23 to 30, as well as those under 12 months.
The proportion of people in England identifying as Christian peaks at age 89, at 78.9%, while for Wales it is age 99, at 82.1%.
At every age in England up to 18, at least one in 10 people is recorded as identifying as Muslim, ranging from 11.7% of one-year-olds to 10.5% of 18-year-olds.
But in Wales the equivalent figures for people up to age 18 range from 4.5% for one-year-olds to 3.2% for 14-year-olds.
The proportion of people in England and Wales identifying as Hindu is highest among 38 and 39-year-olds, at 3.0%.
For people identifying as Sikh, the figures peak from the ages 36 to 44 at 1.2%, while for those identifying as Buddhist the peak comes at the ages 42 to 48, at 0.8%.
The peak comes at a much older age for people saying they are Jewish, with the highest proportion (1.4%) not being reached until age 97.
The census allowed people to write in the name of a religious group that was not part of the main list.
Among those who wrote in a group, people in England and Wales who described themselves as “Yazidi” (413 people) had the youngest average age, at 27 years.
The oldest was for those who identified as “Brahma Kumari”, at 61 years – though this is a very small group (235), accounting for less than 0.01% of the population.
Among other small groups, the average age for Rastafarian was 42 (5,950 people); Jain 43 (24,990 people); Pagan 43 (73,735 people); Scientology 45 (1,860 people); Taoist 45 (3,725 people); and Druid 53 (2,490).