- He's got a mighty deep voice for an 11-year-old.
- He matured early.

7 seconds sound clip from Batman (1966) - The Cat and the Fiddle (S2E3) TV Series.

You can hear this line at 00:11:17 in the Blu-ray version of the movie.

Quote context

[...]

- I'm studying to be an accountant at night. Can't raise three kids on this salary.

- Oh, you're married. How nice for you.

- Canary to cat. Canary to cat. Bat has flown the belfry. Escaped the aluminum reflector.

- Curses, foiled again. Tsk.

- Oh, that's my 11-year-old nephew, Marshall. I gave him this little intercom. He likes to play cops and robbers.

- He's got a mighty deep voice for an 11-year-old.

- He matured early.

- Proceed with plan B, notify all others.

- Mr. Zucchini, may I help you carry those, sir?

- No, open the door, then get lost.

- Yes, sir. I'll just see you to the elevator, sir.

[...]