Old age

Her: "Mum, how old is Coco's grandpa?"
Me: "Not sure, he's in his 60s"
Her: "So why does he look like he's in his 80s!"
Me: ...
Her (before I can answer): "Mum, how old is Coco's nana?"
Me: "About the same age as little grandma"
Her: "Then why does she look so much worser!"
Me: ...
I told her it's because they smoke, and smoking makes you wrinkly. I'm sure she will go and tell this to Coco, who will then tell her nana, who will tell me. Argh.