Time after time, I've mentioned the importance of quantifying your accomplishments in your resume and cover letter. It's a tip that applies no matter the job or level of position, but there's one particular time you should steer clear of including a number in your cover letter — when you're talking about your age.
I've seen countless cover letters that include a line that goes something like this: "I'm a 26-year old who's a perfect fit . . . ". While you might see your age as an asset, the employer may not. In fact, they don't want to know how old you are and some may even discard your application because of the fact that you mentioned your age; it has nothing to do with your ability to do the job. If you're proud of how many years you have under your belt, keep it to yourself during a job search. It can only damage your efforts.