Calvin says, “ well, just give me time, will you? I am older than you are.“ what does he mean by this?

There is a "strange trembling light". She feels as though she is moving through a “horrifying void.” Soon Charles Wallace reappears and she can see him, though she feels distant from him, and soon she also sees Calvin again, though it feels as if she's looking at him through a 'shimmering' veil. Calvin says he will get to her.