Guns are not like cars. They don't really deteriorate as they get older. IF they are well maintained, and springs are replaced, a decades old gun can give just as good service as a new one.
That said, I don't currently use an older gun for CCW (when in a state where I can) or for home defense. My oldest gun for defensive use is my 1991 manufacture Taurus 85CH (I don't carry it anymore, but it does sometimes get used as a HD gun). That said, I'd have no issue carrying an old revolver or auto (that proved reliable) for defense. When I had my first year S&W 57, my intent was to use it as a woods gun (it was in too good shape, I didn't feel right holstering a gun that was older than me and putting holster wear on it since it was near pristine for all that time), I did occasionally load up my S&W 19 (P&R) for HD when I had it, my first HD gun was a 1980s manufacture Taurus 82, and I even loaded my 1940s or 50s Colt Police Positive Special for home defense when I had it (and I would have carried it if I was allowed at the time). The only disclaimer, if I get an older gun that is pristine, or near pristine, I might feel bad putting new holster wear on an old gun that made it that long (I'm a history guy, so if it is old or significant enough, I start thinking museum piece, or at least preserving history). However, if it was well loved/used/carried and already has some wear, I would be proud to put my own mark on the gun myself with my own holster wear.
Oh, when I was a pipe smoker, finding a birth year pipe was often something people looked for (I had a birth year Dunhill for a little while). I would love to find a birth year (1970) Colt Cobra, Agent, Detective Special, S&W 19 or 10 to carry (when I can carry).