Hi All,
I plead guilty to believing that many people, especially women lied about their age.
It may well be true that many people simply didn't know how old they were.
I can't speak about other families, but in my family they were lying.

How else to explain why their ages became correct as they grew to old age, when your advanced age is now to your advantage, something to brag about.
Missing a year or so is easily explained, but in some cases 10 or even 20 years too young!
One of my GGGrandfathers gave his correct age on the earlier censuses, but when he took up with a much younger woman, he suddenly became nearly 20 years younger.
I have personal experience as well. I remember the scene when I was about 13. They came to register our family for an election. My eyebrows went up when I heard my father telling the registrar that he and my mother were in their mid thirties. My mother was 51 at the time, and my father 48. Now my father was well educated and certainly knew when he was born.
My mother, who also knew when she was born, used to tell me that she was 10 years younger than my aunt, her sister. I later found out that she was only 2 years younger. I only found out my mother's true age, when by chance, I came across her birth certificate. She was put out at me for discovering her real age.
I am not trying to start an argument, but I think that the age discrepancies could be a combination of some people not knowing when they were born, and others who simply lied.
These are not bad people. I believe that the people who lied about their ages, thought that their age was their own business and nobody else's, including the government.
Regards