About 100 years for a Parker.
My VH 20 gauge was made on a 28 ga frame way back in 1900 and around 2000 it had become loose enough to have it serviced. A gun maker friend of mine took it to Dale Tate ( http://www.daletategunmaker.com/ ) and they brought it back to life with a period recoil pad and my initials on the German silver stock shield.
It should last another 100 years now as I only take it out a couple times per year.

NRA Patron, TSRA, Whittington Center, DWWC,DRSS
Reloading Ballistics App at http://www.xplat.net/