Surveys are open to all age groups. Some surveys may be looking for younger respondents, while other surveys are looking for older. Here's some more info:
Unfortunately, we don't have any control over the qualification process for the surveys. The survey companies have a limited amount of money to pay for people to do their surveys. So they have to make sure that the surveys are done by the people most qualified for each particular topic. Some surveys are looking for people with specific tastes, other surveys may be looking for people in specific places, if the topic is age-specific the survey may be limited based on age. They get new surveys all the time. So the best thing to do is wait a while and try again to see if they find any surveys you qualify for.