I have noticed that too with the ages being different from Census to Census...but I've also noticed wildly different spellings of names too. It's like the Census takers didn't even ask them to prove their birth date or even ask "How do you spell that?". I even had one relative named Clarence written as Terrence in one Census. I'm guessing the Census taker misunderstood but if they asked "How do you spell that?" they would have at least cleared up that mistake.