How plausible is decommissioning an old carrier and using it as a guided-weapons target?
Short answerIt depends on the war situation, available replacements, and whether the navy has enough crews for the ships it keeps.
NotesAge alone does not decide when a capital ship can be discarded. A navy must ask whether war is underway or likely, whether a replacement is available for service, and whether the existing fleet can be crewed. Keeping every hull is not useful if personnel shortages leave newer or more valuable ships inactive. The proposed target conversion is therefore a force-structure decision that balances material life against replacement and manpower capacity.