We talking firearms or guns in general. Hand me down BB & pellet rifles were the first guns. Winchester model 37 single shot 12 gauge w/ full choke was my first firearm. Traded it off for my Ithaca model 37 12 gauge. Once I got married I found one & bought it for the wife for her birthday.
Bought my first about 10 years ago when I turned 21. It's a HK USP compact 9mm. Still have it today and actually put 250 rounds through it yesterday for a total of about 50K rounds. Never had a single malfunction with a and it still remains one of my favorites. Here she is with all her purdy wear marks.
My first gun was a Taurus .357 magnum revolver. Still have and probably always will. Cant beat the reliability of a revolver! My second gun was a Beretta PX4 Storm in .40 cal but I soon traded it for the love of my life, a GLOCK 30 .45 cal. Hope my wife doesnt read this!
AYA side-by-side double barrel shotgun in 16 gauge. I still have it. My Dad got it for me in 1963 from the same place Lee Harvey Oswald bought his Carcano carbine; Klein's Sporting Goods in Chicago. I still have the invoice.
My first firearm was a Christmas gift when I was 17, it was a Remington .22 auto model 550-1 and would shoot short, long and long rifle reliably. It will also chamber and cycle CB longs. After 40 years it now sits in my safe and sometimes still fires a few rounds from time to time. This rifle has stayed with me when almost everything I bought myself over the next 20 years has come and gone. Now anything I get I generally keep.