Lahaina you are generally correct about the noise levels of the different categories of jet engines fitted to airliners. Older planes such as Stage I or II types are only able to continue in service by being modified to reduce noise levels. This can be done by fitting hushkits to the engines or putting on new engines altogether. For instance, many 727s are hushkitted while others have had JT8D-217A/C engines (as on MD80s) fitted on the outboard pylons. Hushkits reduce the power of the engines, though, so that in the case of some 727s winglets have been added to improve performance.
As Astrojets said, though, even hushkitted planes will eventually have to be retired. Concorde is (was) the only exception - it has an ICAO waiver which permits its continued service despite its extremely high noise levels. That is because it cannot not fly at supersonic speeds if hushkitted and, in any case, kitting it is not practical. The small numbers of them in service may also have been considered.
Hop to it, fly for life!