DOCTOR: The Earth isn't my home, Sarah. I'm a Time Lord.

SARAH JANE: I know you're a Time Lord.

DOCTOR: You don't understand the implications. I'm not a human being. I walk in eternity.

SARAH JANE: What's that supposed to mean?

DOCTOR: It means I've lived for something like seven hundred and fifty years.

SARAH JANE: Oh, you'll soon be middle aged.