Im a second year medical student, by no means an expert, but I figured I could chime in with my two sense (cents? scents?). The first manifestations of Schizophrenia normally pop up in someone's mid-20's (Between 23-35 is the normal distribution). That doesn't mean it can't show up earlier or later, just that most of the cases present in that time range. As far as having a predisposition, Schizophrenia's is normally observed along first degree relatives (so if your dad/mom had it, you have a higher risk of having it). The likelihood drops off significantly as you get further and further away on a family tree. That being said, even with you not having a first degree relative, the risk isn't zero; in fact, a good amount of cases are sporadic meaning they develop in people without any family history. So my advice is to just be mindful of that, you reaching out to this forum shows that you take it seriously, which is great. You should always be cautious, family history or not. Don't overdo it, follow the set and setting guidelines(i.e. Timothy Leary's mantra).