" She shrugged. "Once you've been around for a bit, you get to know stuff."
I kicked a stone. "By `a bit' do you mean `a really long time'?"
She nodded.
"How old are you really?" I asked.
"Eleven."
I thought for a bit. Then I asked, "How long have you been eleven for?"
She smiled at me. "

― Neil Gaiman , The Ocean at the End of the Lane