@magicmirror I honestly think it is kinda important for it to actually address the fact that happened instead of pretending it didn't, and I didn't really see it as an "out of taste pedophilia joke" so much as John having a mental breakdown and suddenly realising that no, they didn't know Terezi's age at the time. Back in the epilogues when John gets Terezi's photo they remark make a mental note that they do look a little older but prior to that they genuinely didn't know, only that often times only minutes would pass in between their conversations on Terezi's end.

No I don't think Terezi was underage at the time but I also think part of the point was that it didn't matter, it was meant to show how John was refusing to grow up so the only person John could relate to at the time was the one person who was also not moving on and was younger then him.