Information high lye

What is the different between "Collision Damage Waiver" and "Liability Damage Waiver" for renting a motorhome? - excess liability coverage

I am not familiar with driving a car as large as transmission.However manual, I'll rent an RV to travel to New Zealand, but I do not have enough insurance for rental cars.
I received an email from the owner of the camper and you do not understand some details.

"Our standard is a collision damage waiver (CDW) covers the rental car vehicles and other objects up to NZ $ 1Million.The excess (deposit):
NZ $ 1500, - (for drivers over 25 years)
Years NZ $ 2000, - (for drivers 21 to 24 old)
NZ $ 2500, - (for drivers under 21 years)

What is the link to more?
Why is it differences between older drivers?

There are other options is "discharge from liability for damage
excessive bail and will be reduced:
NZ $ 250, - (for drivers over 25 years)
Years from NZ $ 500, - (for drivers 21 to 24 old)
NZ $ 750, - (for drivers under 21 years)
Should I pay more than NZ $ 16 for the inPlace?