Is it normal for a 13 year old girl to be flat chested?

It's very normal for a thirteen-year-old girl to be flat-chested, I should know 'cause I am flat-chested - but I'm twelve. Basically you need to drink plenty of water and ask your mum how old she was when she started her period and when she started to grow breasts, because you will start around about the same age as your mum.

I'm fourteen and I have very small boobs - I'm a 28AA or something, I just wear padded-out Bras, LOL. It's nothing to worry about. Try drinking lots of water, and exercising your upper body.