I made a small analysis of this topic and there is no people answering who were between 16 and 21 years. The most people have between 23 and 26.
I'm going to theorise. Maybe between 16 and 21 is the major time of Dark Age when there is one, because not everyone has a Darke Age. But when you lived one it's about between 16 and 21. Some start younger or older (mine was 16) and some end before or after(mine was 23), but it's about this. And another thing who confirm my theory is that jeff_o_rama is 21 and said he just coming of of it's dark age.
Secondly. The fact that most people here are between 23 and 26 is that they started mostly with 1984-1988 castles. People older than this started mostly with 1978-1979 castles. So the 1984-1988 line was very succesful and it explain the amount of people between 23 and 26 years old.
So I guesse that there is many Lego Castle fan between 16 and 21, maybe more than those between 23 and 26, but they are in Dark age.
Soon they will appear in the community...