I have noticed many successuful people in SFI which are over 50.Years are not the reason for succeess or failiure.For exemple, we may have one affiliate who has 20 years old and he don't read,don't log in every day,don't promote SFI ect.On the other hand there are affiliates who are over 50 or 60 years old but they are very active with SFI.Older affiliates have more experience,probably more contacts and friends and that fact can help them to build SFI business.
Hope this help