Not every important character is going to be introduced in the first act. Can you imagine what life would be like if it worked that way? Imagine if anyone that you would ever have an emotional attachment to you met by the time you were twenty. A lot of folks would probably end up marrying their high-school sweethearts, all the quiet ones would be doomed to a life of loneliness, and not many people would ever end up having kids. But at least life would be simpler.
People aren’t supposed to be treated like they’re Chekov’s Gun. You’re never really sure who’s going to end up meaning something to you in life, or when they will. It’s never too late to start meeting people, or too early.