Does anyone know if glycogen level in the body or its ability to store changes (drops) with age?

Most glycogen is stored in your muscles so as your muscle mass decreases it's likely the glycogen storage would decrease as well.

Luckily your muscle mass can be maintained by weight lifting in the off season. My thighs measure and look about the same as when I was in my 20s.

I would try the other section, the 50+ plus riders. Their collective experience might tell you about changes in nutrition and training too.

I think you're asking for a scientific answer. Most riders may not be qualified to answer in that way. My guess is that bike performance and aging is not isolated just to glycogen.

The absolute quantity and quality of glycogen in your muscles are determined by your genetics, post recovery mangement and age. Recent literature shows Efficiency of metabolism (of glycogen) in muscle declines slightly with age and is offset by the relative increase in importance of oxidative (fat) metabolism. The up side of this is that older muscles produce less lactic acid (and are generally less sensitive to fatiging effects of lactic acid accumulation). This is part of the equation of why muscles show a drop in power with age but can maintain endurance with training. There is no evidence that the kinetics of glycogen synthesis in muscle changes significantly w/ age. However what counts is muscle recovery- which is a complex process involving more than just glycogen storage. And for those of us who are long in the tooth... yes, efficiency of recovery drops with age.