The shelf life of a golf ball depends a lot on which type of ball it is. The solid rubberized plastic balls typically found at miniature golf courses and driving ranges could last five years or more, since it has very low compression and tends to stay "in round." The debate over the shelf life really begins with the older model known as a wounded balata ball.
A balata golf ball used to be the standard bearer of the modern ball. In its center was a liquid-filled rubber sphere, which is really the engine of the ball. A generous supply of elastic thread was then wound around the core to give it more elasticity and compression, or the ability to rebound from a hit. This elastic thread was wound very tightly to maintain tension. The entire ball would then be covered with a very strong casing with dimpling for better aerodynamics. Golfing experts suggest that an older three-piece ball might have a shelf life of two to four years.
The reason a three-piece golf ball has a relatively short shelf life is due to the nature of the elastic threading. After a balata golf ball has been used by a player a few times, it could begin to fall out of round. The wound elastic threads may also begin to lose some of their initial tension and elasticity, causing a measurable loss of yardage on drives. An older three-piece ball often does not have the same amount of energy return as a newer one, and there is every chance the outer shell could become nicked or sliced during play.
The modern replacement for the three-piece balata has an estimated shelf life of at least five to eight years, depending on proper storage conditions and amount of use. A solid rubber ball has largely replaced the older fluid-filled core, and many of the newest balls use advanced rubbers and plastics to provide the same tension and compression. As long as the new golf ball sleeves are stored at room temperature, they could conceivably last as long as the golfer who uses them. Once a ball begins to show signs of damage or loss of yardage, however, it might best to switch to a newer one. Damaged golf balls can do damage to club heads, and the replacement cost of a club face is much higher than the cost of a new sleeve of balls.