As someone who’s in their 30s, I myself had forgotten most of my teenage years. I don’t remember much who were my gradeschool or hs classmates and things that happened back then. So, it’s valid that Jejin must’ve forgotten someone or some people from his past BUT if it’s someone who he has interacted or been close with like Taekmu, I highly doubt if nothing happened to him to have lost that memory. Something definitely happened.
As someone who’s in their 30s, I myself had forgotten most of my teenage years. I don’t remember much who were my gradeschool or hs classmates and things that happened back then. So, it’s valid that Jejin must’ve forgotten someone or some people from his past BUT if it’s someone who he has interacted or been close with like Taekmu, I highly doubt if nothing happened to him to have lost that memory. Something definitely happened.