About the 1900 census. Found this in an old newspaper

[shraby]

and I didn't know it was a problem at the time. Guess it was, so those of you who are doing a family tree, here's a clue as to why the ages sometimes are messed up. Women were the main culprits then and they haven't let off since.

Women will be obliged to give their correct age in the coming
census. The new law says: "Women who refuse to tell their ages
or indulge in inaccurate statements thereof, as well as all
other persons refusing to reply to questions or making false
statements, shall, on conviction be fined one hundred dollars."
Manitowoc Daily Herald, Manitowoc, Wis. Saturday, May 27, 1899 P.2

[sybylla]

1. I always figured that was the problem with ages

That or the census taker was easily confused (sometimes kids don't match the proper age, etc)

Many of my female ancestors couldn't even be consistent. Every census they seemed to have a different birth year.

[CBHagman]

2. Amused to hear about that announcement.

But it's not just the Census. There seems to have been a huge amount of lying about ages in my family.

That said, I think in some cases people just weren't sure of their exact ages, and/or the source for the information was faulty. Weren't some Census lines filled out through second-hand accounts, neighbors and the like?

[frogmarch]

3. Emigrants coming to America

often lied about misrepresented their children's ages to get lower fares on ships. This is thought to have happened often during the Great Migration of 1630-1640, which brought many English families - mainly Puritans - to Massachusetts, and it was probably commonly done long before that too.