Sue- 5 to 10 years is really not that far off when you think of the ages people gave on census records (and they should have known how old they were!).
When I was 17 my grandmother died and I remember her 3 sons giving the information to the registrar for the death certificate, They kept asking me for the answers to the questions and when they got to the question 'where was her father born?' I was finally put on the phone. I said 'Liverpool' because I knew his parents had lived there. A few years later I discovered his parents had only moved to Liverpool when he was ten years old and was annoyed I'd given the wrong information. However, more recently I found that my great-grandfather was probably born in Liverpool (at a relatives' house)! Goodness knows who is listed as the informant for my grandmother's death certificate since there were so many of us on the phone that day.