In a 1 page skill based resume, what tense should I use? For example, under Marketing, I've listed 5 skills - 3 were used in the past whereas 2 are being utilitized in my current job.
Is mixing past & present (though accurate) wise?
Are they your current skills? For instance, if I was a mad soup chef in the past and am currently a master steak chef but haven't cooked soup in years and if asked too was unable too then no don't list it. However, if you HAVE the skills and are able to do them then list them.
Don't list anything in your resume you are uncomfortable being asked about or performing or being tested on, if you are and they are beneficial skills to the job you are looking for then yes, by all means list them.
Skill based resume - what tense?
While the strength of a skill may fade with time, generally skills don't disappear completely - you either have the skill or you don't. It doesn't matter if you currently use that skill or not.
In my experience, skill-based resumes are written in the present tense.
If you find yourself agonizing over a skill that was used so long in the past you wouldn't know how to do it any longer, that's a sign that you should leave it off your resume.
You are going into excessive detail. If you used skills several years ago, your skills are somewhat rusty but you can get them back with a minimum of practice, simply list them as current skills - By the way, the only skills that matter are current skills.
Don't clutter your resume with obsolete skills and skills that no longer have any relevance to anyone anymore.