People seem to have chronic uncertainty about my age - when I was seventeen I was in a pub (tut tut) and met a guy who was sort of flirting with me and asked how old I was. I told him, and he looked surprised. Another guy said "yeah that was my reaction too, I thought she was a lot younger!" and the flirty guy said "no, I thought she was in her twenties!".
Got the same thing with the kids in Paris; on the first day I dropped the younger girls (4 and 5) at school, people assumed I was their mum. When I took the 12 and 6 year olds out to lunch the waitress asked me where my mum was.
Basically age is meaningless and we should all just forget about it.