First of all I would ask why you would want to restrict yourself to a specific age group when trying to get active affiliates?
Personally I take and treat most of my affiliates in the same way.
There are many ways of attracting affiliates to sign up to SFI as it is free, but the problem is turning those free affiliates into active affiliates.
I believe a lot of the advertising that is done for SFI does not give the potential affiliate the information they need to make an informed decision before they sign up. For example what they need to do on a daily basis and the amount of reading they will need to do if they are going to learn the system and become successful.
Tell your potential affiliates from the start that although sign up is free and they can remain free for life that if they want their business to progress at a reasonable rate then they will need to make a monthly outlay.
Inform your affiliates that they will need to spend time daily on working their business if they want to become successful.