Old vs tall

How can someone short be old - that's Naisha's latest query. According to her as one gets older they just get taller. The idea that people stop growing taller at some point is alien.
I was telling them the story of Snow White and the Seven Dwarfs. When I came to the part where Snow White is 'dead' and the dwarfs are watching over her Naisha came up with an addition saying, "Woh log toh school bhi nahin jaa pate the." Then I had to explain that they were old and didn't go to school. Then followed a host of questions on how come they were old but were not tall (She'd seen pictures in her book).
Concepts which seem so simple are sometimes not so simple to explain.