I assume you are talking about someone other than yourself? Most 19 year old males are quite strong physically and could pose a threat if they tend toward violence when not on antipsychotics. In most cases, though, people with schizophrenia are not violent toward others -- they pose a more severe hazard to themselves than others if unmedicated. But if you are concerned about this person, share your concern and offer to accompany him to the doctor of his choice, preferably a psychiatrist.
Carolyn