I agree that this poll is not scientific . The average age for PCa is late 60s whereas this poll shows much younger.
I can think of several reasons for that. People in their late 60's as a group are less likely to go to forums. Also, more aggressive types of PCa would tend to show up at an earlier age prompting those younger people to seek input due to the depth of their concern.
Polls in any forum tend to not be scientific due to the skewed interests of the membership.