Welcome to SA!
I admit many of my active RPCs are currently above Greyson's age, but there are two that are of/close to his grade level:
Noel Florian - She is probably the best candidate. While also fairly shy, her development has helped her get to the point where she can at least approach someone in a one-on-one situation. Additionally she has a lot of issues with her abilities but is working towards figuring out just what she can do. She could be a source of comfort/relation since she's only a bit ahead of Greyson when it comes to experience with....well, Manta Carlos madness in general. Plus she's within his age range so they could regularly end up in classes and whatnot together.
Troy Abis - Looks scary but is really sweet. He's incredibly laidback and chill with pretty much everything. He'd be a good listener and would make very few requests/demands. He's also pretty quiet though.
A third option:
Wakanda Voltaic - The most outgoing of the three choices. She'd be a rather weird one thanks to her behavior, but she's very friendly and would likely take an advisory approach towards Greyson. However, much of her own issues relate to her powers, so she wouldn't be completely detached from his experience/problems. The real issue with this one is she's eighteen and out of school. Considering the fact she wanders pretty much everywhere, they would have to somehow run into each other somewhere within the city. Not difficult but might rely heavily on coincidence.
I organized my signature to include all of my RPCs and to also include threads such as my plotter. For convenience's sake I will link the plotter
here for you to check out. If you like something you see, then feel free to let me know via the method that is most comfortable to you.