King Daniel Into Darkness wrote:
The Klingon D7/K'tinga design has been used for at least 225 years (first appearance: ENT: "Unexpected" in 2151, seen throughout TOS, TNG and DS9) and the Bird of Prey for almost as long. Although I don't know how long each individual ship is supposed to last. Their rusty, worn out appearance suggests they're very old.
Indeed, however "design" doesn't mean "ship".
I always felt that the life of a particular starship design didn't always match up with the life of a particular vessel.
The Galaxy-class may have a design life of 100 years--and maybe one or two of those ships may come close to that--but other ships in that design may be retired far earlier depending on individual circumstances. In "All Good Things...", the Enterprise
-D was going to be decommissioned after less than 25 years of service. Conversely, it's possible that the NX-class continued for many decades after NX-01 Enterprise
was decommissioned, and her retirement had nothing to do with the design, IMO.