Technically speaking, life jackets don’t have an expiration date. Practically speaking, however, their material does tend to lose its ability to maintain buoyancy with frequent wear.
As a result of the wear and tear of the vest’s material, the performance of the jacket starts decreasing (which isn’t what you want when stranded in the middle of the river). For this reason, try your best to keep your life jacket in a dry and cool place and check for signs of abrasion after every use.