Also if you are prone to developing a psychotic disorder (prevalence of psychotic disorders is ~3%), pot consumption before the age of 20 increases the chances of it happening.
There are plenty of sources and the original papers are easily found, but there isn't a proper bibliography with links which I agree is frustrating. For example the first one says the last name of the author and the year: Andreasson and 1987. So I googled "Andreasson 1987 cannabis" and found the article: