No great surprise to me. The responders present a bimodal distribution centered in the 20's and 40's.
The increase in interest in the teen years is evident, but young folks typically don't have a lot of disposable income, and have many other interests and distractions.
My speculation is the peak in the 20's probably represents those who have finished school, have started working, have some disposable income and don't yet have kids.
The dip in the 30s is most likely the result of the economic reality of having responsibilities such as a home, significant other and/or children resulting in less disposable income and much less free time.
The peak in the 40's probably represents those folks who were in the hobby before, spent their 30s raising children, want to get back in the hobby and want to get their teenagers interested in something other than computer games.
The slow fall-of in the 50's and 60s probably represents those of us who like rocketry and never grew up, have disposable income again, and have grandchildren.
Bob