Question about Pacifiers

This is probably a dumb question about pacifiers (AKA soothers, binky or dummy if you're from other parts of the world).

My son turns two months tomorrow (holy cow!) and I've decided to give in and try using a pacifier when he's screaming in the car. I'll probably get the Philips Avent brand, but noticed they have a size 0-3 months then 3+ months on Amazon.

Which one should I get? I know the obvious answer is 0-3 but not sure if nipple size is dependent on age or mouth size?