When do people first start using cannabis?

The average age for starting to use cannabis in Western countries seems to be around 14-15 years of age. It appears that the average age of first use in developing countries may be a bit older, but it's hard to tell because there's not much information. The idea that cannabis is a gateway drug that leads to other drug use has been proposed for years. It remains a controversial idea, because while it is true that most users of other illegal drugs (e.g. cocaine, heroin) have used cannabis, the vast majority of young cannabis users do not use any other illegal substance.
Some other points:
Age makes a difference: In the higher-use Western countries, recent use increases from under 5% in Grade 7 to 30-40% by the later grades. Gender makes a difference: Boys are generally much more likely to use cannabis than girls, although as with tobacco and alcohol, the gap in several countries is closing. Boys are more likely to use frequently and heavily and (according to one study) in public places. Social and economic status makes a difference: Street youth are more likely to use cannabis and to use it heavily than are "mainstream" youth. But even among mainstream youth, heavy, risky use is not unusual. One study in North America showed that one-third of youth between 14 and 17 years of age had used an illegal substance (mostly cannabis) more than five times, and among them: