Agreed that they're very likely underage. Plus, excerpts from their writing, which started out as an attempt to write themselves into the Foundation'verse as a kid with claws and a murder streak:
SCP-XXXX is what looks like a Japanese/European male ██ yr old. It is capable of higher speech and is very vicious. If there is a human in its light of sight, it will viciously leap forward, and with its claws, [DATA EXPUNGED] and [DATA EXPUNGED] Its victim.
SCP-XXXX is what looks like a Japanese/European male unidentified- species 15 yr old. It possesses human-like features except for its mouth. SCP-XXXX's mouth opens 6 times the average human's. This seems to be a feature used for eating its victims easier.
SCP-XXXX is what looks like a Japanese humanoid ██ year old. The only feature unhuman-like, is it's similarity to the Japanese, yokai. SCP-XXXX does not possess ghost-like abilities, the exception being its mouth and ability to spiritually heal.
SCP-XXXX has no way of killing, only if it teleports into another organism, causing the organism to implode causing a bloody mess. SCP-XXXX looks to have curly brown hair along with hazel-colored eyes. It mostly walks around bearing skinny jeans and a sweater.
Also, they refused to state their grade in school because "I don't like to share any personal info. It's not that I don't trust you, it's because I'm very cynical."