There are not too many more nightmarish scenarios than realizing when you need it, that your life jacket no longer works. This means that yes, they do have an expiration date. However, this should not come as much of a surprise to you because nothing lasts forever. But, it does not work like a food product. When you use it the first time, there is not a date on the product that informs you of when it will stop working. As with anything, life jackets are susceptible to damage over time.
When the material inside of the jacket, which is used to provide proper buoyancy to keep your head afloat, becomes damage it will hinder the performance. In due time, it will recede to the point where it is unusable. It is hard to prevent normal wear and tear, but there are some precautions that you can take to prolong the shelf life of a life jacket. The way you store it, which will be addressed shortly, and how you use it (do not use it for anything outside of its intended purpose) could be deciding factors in how long the jacket lasts for you.