Nothing too old, as the oldest shotgun, rifle and handgun I have fired are roughly 100 years old or so:
My inherited Winchester Model 12 16 gauge shotgun dates from the early 1930’s. My Mother’s Grandfather bought it around the time he bought the family ranch, which was purchased a few years post-depression.
My inherited Remington Model 4 .22 LR is from roughly 1915-1917. It was my Dad’s Father’s first gun, he got it as a kid to hunt hares-rabbits for food in the Nevada desert. (He, his brother and my Great-Grandparents arrived here in the USA from Scotland in 1912. They mined gold in Searchlight until the mines petered out.) That gun has a lever for takedown, which was discontinued in 1927 and replaced with a takedown screw.
Handgun-wise, my Colt Officers Model Heavy Barrel .38 Special revolver dates from the late 1930’s.
Stay safe.