Well, I wasn't into them when they were teeny-boppers, but I think they started their careers in another group, around age 10 or something.
Definitely early 20's is young... but not underage. And their vibe these days is more spears & battle-flags, rather than lollipops and stuffed bears.
The mixture of Kawaii (cute) and Metal (not cute) genres is something that I found interesting...
Now if I'd put up a video of AKB48 or something, then I might have to concede your point! ?