I thought you thought she was younger but nope she's a legit 18, she just has always looked older.
A lot of the dancing places you see are just hired talent and don't work there irl so it's possible this is the case originally as well but idk.
The stuff she posts doesn't even surprise me, japan has a problem with parents "legally" pimping out their daughters to older guys for gravure etc...
iirc it's bts livestreams of them cooking, q&a style with no masks etc... but might have changed since the last time I saw it.
Side note, the mom's kinda hot though ngl.