Black Powder has an extremely long 'shelf-life', if kept in a relatively dry environment. It is a mechanical mix of sulphur, charcoal, and potassium nitrate, so it is not subject to the chemical deterioration that happens with time in smokeless powders.

The 4F granulation is intended for priming the pans of flint-locks. I guess Life is telling Paul to get a Flint-lock!

FWIW - In my silly years, I had several pounds of 4F Curtiss & Harvey powder, which I used up in 45 grain 'Skirmish/Target-Loads' in my reproduction .58 cal. 'Zouave' percussion ML rifle. I also fired 4F in a brass frame replica percussion revolver. Nothing unusual happened and function and accuracy seemed normal. Maybe, Angels were looking over me.

I wouldn't do it now. I am certainly not recommending anyone test fate. Back then, I did not know any better.