I'm only posting this for the record since I confronted him on this and got him to outright say it.
While I get what criacuervos is saying that, there could be some uncertainty since we're talking about someone who is only posting written messages, I don't think that RJ was lying about his age since a lot of his behaviors did line up with some kid who has some sort of learning or social disability. This also isn't the first time he admitted that he was underage or in the fifth grade either.
It may have not been right to confront him, however the circumstances surrounding the situation warranted it. EDIT: If anything I'm holding onto whatever screenshots I have of my interactions with him simply because if he follows me elsewhere I still have leverage to point out what issues I had with him and why I want nothing to do with him.