licence for car hire

Hi all,
another question, LP book says you need an international drivers licence to hire a car, but on some hire car web sites, they say just a current licence from your own country is all you need, as long as you are over 25, so what is correct?
thanks

I would also be interested in the answer to this as my boyfriend and I have considered car hire. He would be driving, however he's only 21.

We have always just had our NZ drivers licence. Not sure about the 'over 25' rule though - way past that!