Reddit and even HN currently I believe do not account for age bias. Upvotes have a cascading effect and posts which happened to get a few votes early tend to out compete all other posts. What I'm suggesting is to have a small quota on the front page purely for experimentation. These experimental posts do not need to compete with other posts for visibility and the outcome from them can be used to calculate interest. Since these experimental posts are only competing with posts within the experimental set, there is fairness with respect to age and viewership.