Pianogurl's birthday

When Pianogurl was 12 and wanted to read the Twilight series, I told her she had to be 15 first. Now that she's turning 15, she's trying to take me up on that. I told her she isn't old enough, which of course brought on the, "But, Mom, you said..." To which I replied, "Well, when I said that I didn't know you'd be so young when you turned 15!" Where does the time go?

 How does one of these...

turn into one of these?