Because 30 is too many!
they're too mature for their taste
An ambulance.
Motorist: So I could race home to get my license and registration.
Turn 19
A barber.
One, but they'll take 30 visits to do it.
Lord of the Rings
A: Because 36 would be too many.
30 - One to hold the light bulb and 29 to drink until the room spins.