Does a Iphone 4s need a micro sim or nano sim?

My brother got an Iphone 5 so I'm going to be using his Iphone 4s. It's with telstra and is prepaid. Just wondering what sim card I needed and if I need to be 18 to buy one?

I believe it is a micro sm card, but you can go to your cellphone service provider and ask them exactly.

MicroSIM. If you just getting a SIM any age is fine.