Scents will last for decades if they're in spray bottles, properly stored out of light, and in a cooler place. Some members keep their scents in the boxes they came in to keep them out of the light, some don't. I've got a couple 20 year old bottles that smell fresh as when I wore the scent long ago and fresh as the same scent in new bottles.
This is a frequently asked question and I'm sure some searching will turn up several threads on the subject (the Just Starting Out board probably has some more recent ones) and you can read plenty of members talking about this issue by finding those threads.
Hope this helps.