That's right, it has nothing to do with age, it's the inherent design of a free-floating firing pin. When the pin becomes stuck forward, the action will cycle and fire every round in the magazine until it's empty, as fast as that action can physically move. Some SKS's did have a spring loaded firing pin, and there are aftermarket conversions to convert to a spring loaded firing pin, but for most people the easiest thing to do is just check the pin for free movement on a regular basis and keep it clean.