I’m not convinced this is a good idea. The date of the last edit is a poor indicator of how complete and relevant a wiki page is. There are plenty of packages that are still maintained and work fine but are not under active development (i.e., the ROS API is stable), so there is no need to update the wiki page. On the other hand, there are also plenty of new packages with shoddy documentation. As a maintainer, I’d prefer to get emails (or better: GitHub issues) pointing to specific flaws in the documentation than just “hey, I got this warning message telling me to ask you if the documentation is still up-to-date. Is it?”.
Also, by my guesstimate, for every 10 users that run into a problem, there’s at most 1 who actually contacts the maintainer. A warning like this would probably just create the impression that 90% of the documentation on the wiki is outdated, and newbies would be more confused but not feel confident enough to actually contact the maintainer, so the maintainer wouldn’t even be aware of this problem.
Welcome to the community and thanks for making it better! I don’t think anyone will be offended by suggestions (and actual pull requests) for improvements.
As an aside: You are absolutely correct that there is often a mismatch between the documentation on the wiki and the actual code. In recent years, I’ve moved most documentation of my packages from the wiki to the GitHub README. This makes it easier to actually keep documentation and code in sync.