What does it mean when a girl ask you how tall you grew?

Answer 1

She wants to know how tall you are, maybe she likes tall guys, or possibly shorter guys, even more likely she wants to know your height so she can decide what size heels to wear so that her height more closely matches yours when you are out.

Answer 2

It could be a way of showing interest in your growth and development, or it may be a casual conversation starter to learn more about you and your physical attributes. It could also be a way of making conversation if they remember you from when you were younger.