Probably depends on where your "shelf" is. I have heard that under ideal temperature and humidity conditions the solid core balls will show minimal degradation over time. I would think that would not be the case if you kept them in the garage or trunk of your car and they were exposed to extreme temperature variations. What you will not get is advances in technology of newer models so unless you just love a specific year and model of ball, I personally would minimize my stockpile and upgrade as new models are released.

The solid core balls decline more from storage conditions than from age. My garage goes from -5F to +95F, so no golf equipment is stored there. Same for when my car is parked outside. The trunk temperature can easily exceed +120F. If stored in a closet, then 10 years would be reasonable.

With advances in design, the performance from 5 cycles ago will be different than the current, even with all else equal. You can make a decision to keep or donate to a junior golf program after a certain amount of storage time.

Should the USGA follow JN's recommendation and try to disarm BdC by rolling back the ball, ...wait a minute. That will harm far more than 95% of all golfers. I'll consider laying in a supply of balls to use for years. At age 70 I can't add 40 lbs of muscle to regain my current distance. Just because Aaron Rodgers can throw the ball 20 yards further than Sid Luckman or Sammy Baugh, or field goal kickers are longer than Lou Groza, football didn't lengthen the field to accommodate. ....Sorry for the sidebar....too much coffee.

Have answered this before and was told by golf industry people that solid core golf balls that are stored at room temperature have virtually unlimited shelf life.

Better use them up before the big bad usage makes them illegal!