Such as things they enjoyed doing, etc?
My mum is completing a Grandparents Book that we bought her to do for ds, and she keeps saying "Well I can't remember any of the bits about "your mother (i.e me F&Z)'s childhood", so I will have to ask you when I come up."
I am 35 so I suppose it was a long time ago. She is 70 odd and neither wildly on the ball nor very prone to forgetfulness.