Perfumes do expire but if you keep them properly, they will last for many years. Many fragrances can last well beyond five years depending upon where they were kept and what the fragrance composition in the perfume was.
Generally, perfume's two biggest enemies are heat and light. Air is another factor but if your fragrances are in spray bottles, air is less of a problem unless you unscrew the cap and let the air in. In general you should keep perfumes in a cool dark place where temperatures do not fluctuate too much. So don't let them sit on your dresser in direct sunlight, don't store them in the bathroom where the temperatures fluctuate a lot, and don't put them next to a heater, or let them get so cold that they freeze.
There is no set expiry date for a fragrance as the factors that lead to expiration vary wildly depending on how the fragrance was stored during its lifetime and what went into composing the fragrance in the first place. Expiry dates are a suggested use by date but often times a well-composed perfume can last a very long time. An improperly stored fragrance may only have a shelf life of a year to two years. A well cared for and properly stored fragrance can be beautiful even fifty years down the road.
One of the ways you can tell if your fragrance might go bad sooner than other fragrances you own is to look at the notes. Citrus notes are notorious for being volatile and will usually be one of the very first to break down. So if you have fragrances that rely on a lot of citrus, I would take extra care in storing those perfumes if you want to retain their original scent. Some notes, however, are more resilient such as musks and resins. It's really a very wide berth between which perfumes last and which ones don't. For example, Clinique's Happy tends to deteriorate (if stored improperly) within five years. Whereas some bottles of Chanel No. 5 are over sixty years old and still smell the same as they did back when they were fresh.
So, in short, how long a fragrance lasts and when it expires varies wildly. All you can do is take care to store your perfume in a cool dark place. If your bottles have been in the closet since 2008, they are probably still fine. You can do a visual inspection to make sure, a perfume will have changed if it's gotten darker than it used to be then you know something's changed in it.
The best way you can tell for sure is to spray it and smell it to see if it still smells okay. If it doesn't smell like how you remember or if the scent no longer appeals to you then get a new bottle. If you can't remember how it smells, make a trip to the department store and see if you can find a tester bottle that you can spray onto a piece of paper to take home and compare, take a clean piece of paper home with you too because perfumes often smell different on the skin than they do on the paper. Better yet, ask the ladies at the department store if they can give you a sample of the perfume and you can go home and double check that way.