Why 7 is different than 17

We finally got around to some much needed winter clothes shopping this weekend. As Athena and I were riding to school this morning, her wearing one of her new shirts she says to me "I think Bailey has this shirt but it's pink, I can't wait to show her. Maybe we can wear them on the same day" Now if Hailey even sees another person at school (or anywhere actually) with the same shirt as her it is tucked away deep into the closet never to be seen again. Weather she knows this person or not! So I'm wondering at what age this shift happens, where wearing the same shirt goes from cool to very, very uncool? But I have been wondering about a lot of things these days. Man I am getting old.