Do you really need a poll for this? Just like every other tech site it's a bunch of 18-35 year old dudes sitting around clicking reload every 20 minutes.
I think you underestimate at least the top end of that age range. I am quite certain that a number of folks on HN are well above the age of 35. PG is in his 40's, and I'm sure he's not the only one here in that category (and I wouldn't be surprised to find hackers older than that here -- perhaps much older).
Now THAT would be an interesting poll
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It's been done. A little over 8% of respondents were 40 or over.