Homestuck has existed for ~16+ years. Some people have been around longer if they started with Problem Sleuth's original run (or earlier.) I mean, Hussie (author and original creator of Homestuck) is 46 and has been making shit for a long time.

While there are a lot of teenagers running around in the greater Homestuck ecosphere, it's still likely got a pretty even split between age groups just because of how long Homestuck has been around; I was once a terminally online teenager reading Homestuck, now i'm 23, still terminally online, still like Homestuck. 22 isn't old in general and it certainly isn't 'old' around this fandom. If anyone acts otherwise they're being purposefully dense.