Parenting

As a father how do you adjust to the changes in your children as they get older? Especially if you have girls. Today my wife says we will soon need to get M a training bra. I say what? As she is only 7 and my wife says haven't you noticed she is stating to get bigger and things are starting to form? I can honestly say yes I new she was getting older and her interests are evolving but NO I never noticed the hormonal changes.
As I think about it I am dreading the next few years because we all know what it's like to start dating and having that first crush. She has not started that yet but it's not to far off as she is now into music and the current style and of course starting to show interest in boys. When she sees certain guys on TV she says they are cute her face turns red and she lets out an embarrassed giggle. She already spends as much time on the phone as a teenager.
What is a father to do? I don't know if I'm ready for this but then is any parent ever ready?