I am 33. I live in the US. I am a neither a US citizen, nor a green card holder. I have worked in various jobs as a research assistant (physics, biology, economics) usually involving programming, mathematics or statistics. As a newly minted undergraduate, I didn't really have much confidence in myself and I completely ruled out graduate school as pointless. I didn't think of myself as smart enough. I drifted into working in labs, because those are some of the easiest ones for which one can get a work permit in the US as a non-American.
Having worked in academia for a while now, I've had a chance to leap into various fields and help build solutions to complex problems. I think I have literally gone as far as I can go researching in academia with no higher degree. I work at one of the top universities in the world. (If you looked at US News rankings or the Academic Ranking of World Universities, it's in the top 5.)
Lately, I've been thinking about applying for graduate school. I do have a few papers in various fields. I'm thinking of a PhD in either pure mathematics, applied mathematics, statistics or computer science.
I see two big minuses to applying to graduate school:
Most people applying are more than a decade younger than I am. (Alas, more than a few gray hairs have made an appearance in recent years.)
Perhaps my achievements would look good for someone younger, but partially my achievements are the result of a long career rather than any special brilliance. So, I wonder how my record will be perceived. I did take GRE and I scored 800 quantitative, 800 verbal and a 5 on the essay. (I would most likely have to do a GRE subject test depending on what field I ultimately decided.)
Please advise on how accomplished, but older candidates, are viewed in the graduate school application process.