Possibly. There is a lot of research on this. What is known is that people (usually late teens) about to have their first psychotic episode often begin using or increase the use of marijuana. Unclear is the cause of that connection. Perhaps emerging psychosis changes values, leading to new activities such as marijuana use; or perhaps marijuana has an effect on the brain, speeding the psychotic process.
Yes, earlier onset. Research results seem to show that marijuana (pot, mj) can start a person's schizophrenia sooner than if he did not use mj. A teenager (with a brain, neurotransmitters, & receptors not fully developed), especially with a family history of schizophrenia or psychosis, should know his family history and avoid experimenting with mj or other illegal drugs that might have a similar effect on the brain.