Building Engineer: Aren't you a little young to build a rollercoaster?

Phineas: Yes, yes I am.

Building Engineer: Well I must say that I'm really quite impressed,
but all your permits are in order.
Don't forget the bricks and mortar
and if you need a power loader, be my guest.
But if I'm pressed,
I'd say you look a little young to drive a forklift.

Phineas: Yes, yes I am.

Building Engineer: It's good to see a younger guy like you
who's creative and ambitious.
A little bigger than his britches.
And who's got a fresh, exciting point of view.
Yes it's true!
That you seem a little young to do the things that you do,
even with all that moxie you've got.
Yes, you seem a little green
to be controlling this machinery.
Phineas: Yeah, I get that a lot.

http://phineasandferb.wikia.com/wiki
/Aren't_You_A_Little_Young_to_Build_a_Rollercoaster