Nearly one third of UK armed forces veterans living in England and Wales are aged 80 or over, while around one in six do not hold a passport, census data shows.
Veterans are also more likely to identify as Christian than non-veterans, but less likely to describe themselves as single.
The findings have been published by the Office for National Statistics (ONS) in the latest release of data from the 2021 census.
The census was completed by more than 24 million households across England and Wales on March 21 2021, and was the first of its kind to collect data on people who have previously served in the UK armed forces.
The new data provides a more detailed breakdown of the veteran population and looks at factors such as age, religion and ethnicity.
It shows that 32% of veterans were aged 80 or over on the day of the census, compared with 5% of the non-veteran population.
The figures reflect the legacy of the long period of War Service and National Service that ran in the UK between 1939 and 1960, the ONS said.
National Service was a system of conscription that required healthy males aged 17 to 21 to serve in the armed forces for between 18 months and two years.
It was phased out gradually in the late 1950s, meaning the last surviving people to have done National Service will now be well into their 80s.
While most veterans in England and Wales were born in the UK (94%), around one in six (17%) said they did not currently hold a passport.
Some 2% (39,420 veterans) were born in other Commonwealth nations, with a similar proportion born in Nepal and Ireland (0.6% and 0.5%, or 10,240 and 9,480 respectively).
Rich Pereira, head of demography at the ONS, said: “Today’s data gives a greater understanding of our veteran armed forces community. We can see that almost a third of the community is over 80 and 86% of the community are men.
“Many of this group will be those who took part in National Service and/or served in World War Two. Our data also explores how veterans compare to those who are not veterans with regard to health, religion and ethnicity.
“Today’s insight is crucial for the planning of support and services for veterans and their families.”
The figures also show the vast majority of veterans in England and Wales (96%) identify as white, compared with 83% for the non-veteran population.
After adjusting the data to assume the same age, sex and regional location for non-veterans as for veterans, the ONS found the gap was smaller but still apparent, with 90% of non-veterans identifying as white compared with 96% of veterans.
The difference could reflect a number of factors, including long-term trends in immigration and nationality law and the tendency of different groups to join the armed forces, the ONS said.
Nearly two-thirds of veterans (64%) described themselves as Christian in the census, compared with 48% of non-veterans.
The adjusted estimates are 64% and 58% respectively, suggesting this difference is not just to do with age, sex or regional structure of the veteran population.
Veterans are less likely to say they are single – never married or in a civil partnership – than non-veterans (15% compared with 39%).
Some 91% identified as straight or heterosexual, with 0.9% as gay or lesbian and 0.5% as bisexual.
Once non-veteran estimates were adjusted for age, sex and location, there were no notable differences in the sexual orientation figures between veterans and non-veterans.
The census takes place across the UK every 10 years and provides the most accurate estimate of all the people and households in the country.