Neither do I - 40. Have gone through a film-only intro into photography 24 years ago, onto digital only for about 10 years (2001-2011) to happily doing both.
I think the guys in their 30's are too busy raising kids and shaping their homes and careers around those needs. I would love to know what the gender representation in the different age groups is. It would be great to see +/- 50/50 in the younger categories. I get the feeling that the medium doesn't reach a certain part of the population, at least where I live (RSA).