My mom used to say, "You're as old as you feel." Keep that in mind if you are an older person crafting a resume and cover letter.
A lot of older workers are finding themselves in the job market again having gone through layoffs. There is a way to make potential employers aware of the advantages borne of your experience without dwelling on the number of years you've been at it.
Embrace professional social networking sites
I've cautioned a lot of people about the pitfalls of being too involved in social networking sites, but these days it's almost essential that, as a job candidate, you have some kind of web presence. If you make it clear that you don't go for all that "trendy" stuff, then a prospective employer is going to wonder how open you will be to any new technologies that come down the pike in your day-to-day work. I didn't particularly like the social networking thing myself at first but I've grown fond of it. I just try not to post any sepia-toned photographs of myself slamming back beers with Abe Lincoln.
Choose your adjectives carefully
It's unfortunate, but to some people looking at your cover letter, the word "seasoned" could imply "world-weary." (I was going to say "overcooked" but that seemed a little gross.) "Seasoned" might indirectly imply that technology doesn't excite you and most employers want enthusiasm (at least initially, until they beat it out of you). Instead use words like "versatile" and "adaptable."
Limit your list of experience
I see a lot of resumes from people who feel the need to list every job they've ever had. (Not a good idea, and is precisely why I don't list that summer internship with Henry Ford.) You might think that a long, varied list of experience shows you're well-rounded, but really, it might imply an unconscious desire on your part to cling to the past. List only jobs going back about 15 years. Think about it: Technology changes so quickly that your intimate knowledge of the Sinclair ZX80 isn't going to matter in today's tech job market. State your most up-to-date skills and remove any mention of obsolete technology.
Get a gmail account
If you want to be thought of as cutting edge, you might want to lose that earthlink url.
Here are some other resume tips for older job seekers.