Tags serve to categorize questions, so that:
- questions become easier to search, and
- users may filter for a particular topic they are interested in.
Therefore, we have tags for certain technologies like c#, tags for areas of software engineering like architecture or project-management, and tags for certain software engineering concepts like design-patterns.
In contrast to those examples, a “it-took-a-generation” tag is not helpful:
It does not describe a well-known concept, technology, or sub-field of software engineering. Instead, it describes a rhetoric device used by a single author. Other concepts that were invented by an author have since been picked up by the wider software engineering community, for example the SOLID principles. “It took a generation” is no such widely accepted idea.
It does not help users when they are searching for a solution. I.e. I see no scenario where someone would research a problem but would like to limit the search to posts tagged it-took-a-generation.
This tag is unlikely to have its own community, e.g. people who are only interested in answering questions tagged it-took-a-generation.
To emphasize: This site is about software engineering questions and answers. The questions ask about a software engineering problem, and answers suggest solutions. “It took a generation” is not a useful tag for problems. It would be a good tag for a blog full of “thoughts” and “musings”, but that's not what a Q&A site is about. Please read What topics can I ask about here? and What types of questions should I avoid asking? for further details.
You have not explained convincingly how that tag would be useful for on-topic questions. It is not even clear to me how the suggested tag would apply to your question on the main site.
For all these reasons, I am thoroughly opposed to the creation of such a tag. Thank you for your understanding.