I'm 31. Here is my opinion on behalf of the 30-somethings...
I watch the show for the entertaining HMs, even the immature ones. If I didn't like entertaining/immature/obnoxious/outgoing/flamboyant/wild characters, then I would be watching something else (like my parents do).
Most of the people over 35 who like boring stuff just simply do not watch Big Brother. So, to blame the over 35s for the demise of the entertaining HMs is - in my opinion - inaccurate. I think the blame has to lie at the producer's door for carefully selecting the highlights they show on the C4 show. Some people only get to see it, and don't get to watch much live feed.
Also, it seems to me that since almost all young people have mobiles, that they will use them to vote, so that the phone bill is not an issue. It's not exactly expensive to vote once each week.
I only vote in the final of BB for who I want to win. I never vote in the weeks leading up to it.
I conclude.. I do not believe that the "oldies" are to blame for the show going to the dogs.
PS. I wanted Maxwell to win, I found Kemal funny and I loved Science. In case anyone wanted to know.