Why don’t you get him evaluated if you have custody and have concerns? You don’t say his age but a google search says under 13 is rare and under 8 is considered early onset. More typically it’s diagnosed mid to late 20’s up to 30’s but the sooner you have him seen the better. I just read a headline from Medscape an app I subscribe to stating that cannabis is shown to be a big risk factor for schizophrenia in young men. You’ll have to verify with your grandson.