Be positive!—Showcase the contents of your cover letter in a positive manner. You can have all the qualifications in the world and yet you will still fall short of getting the job if you're note positive enough.
Above all in your resume and interview—you must be positive. Leave out any negative or irrelevant information. If you feel your graduation year will subject you to age discrimination, then leave it out of your cover letter. If you've done tasks and duties in your past or current job that don't support your job search objective, then don't include them. Focus on tasks that are relevant to the job you're applying to, and don't include personal information such as height, weight, or race.