Previously I'd stuck one candle in a slice of cake for my birthday. So she remembered that and told me, Mummy I know you are ONE year old! Because there was one candle for your birthday. The following year I stuck in TWO candles, for continuity, and she remembered that too. (Coincidentally, that was my real exact age minus the decades part, so it was very easy to remember)
That was the good old days. Now that she is 6, of course she knows I can't possibly be younger than she is. So when she asked my age, I told her (rounded it down a bit ahem).
Recently in the car...
(Kids playing with a toy)
Me: Oh I want to play also!
JE: MUM-MEE! YOU ARE FORTY YEARS OLD!!!
JE: Ignore my mummy. She's too old for toys