Grading Skills

I always found "X years experience in Y" or "working with Z since year ABCD" or "EFG certified" not indicative of a person's skill whatsoever. Nevertheless, we still need to keep this style around for automated application screenings based on keywords and numbers.

Skill Matrix

Instead, I propose to grade skill level on further dimensions:

Currently actively learning (solo/team/course)
Productivity, can you create value using this? (guided/solo/team)
Mentoring capability. Maybe explain this further, e.g. how this happens in your team, via code reviews, one-on-one mentoring etc.

E.g. for programming languages:

Skill	Years Exp.	Certification	Learning	Productivity	Mentoring
Python	13	-	solo	solo	FOSS work
Java	14	OCP Java 11	team	team	via code reviews, FOSS work
JavaScript	5	-	solo	guided	-

For tools, natural languages and other qualifications similar tables could be made.

Also, one should probably list, what one is not interested at all in and what one want to learn in the future (learning backlog).

Similar Assessments

Skill Maturity Matrix
Here, probably the most further columns could be derived from.
Thoughtworks Technology Radar