> It could very well be there are older alternative libs that are better

The libyear metric doesn't count when the dependency was last updated by the maintainer. Its a diff of the version you're currently using compared to the latest release, to tell you how out of date your current dependencies are.

Its pretty much a dependency drift fitness function (https://www.thoughtworks.com/radar/techniques/dependency-dri...). Some of the variants on this page do support alternate metrics, like the ruby and node versions which can calculate number of releases behind rather than time.