I want to start by saying I gave a little check to the literature on the subject in order to answer your question. The problem is that to find out if there is a relationship between starting drinking young (what does that even mean? a beer at family dinners?), one has to either ask seniors at what age they started drinking and whether they are alcoholic or not, or do a costly follow-up of a youth sample and follow them up until it is possible to associate their rate of alcoholism with a known life-time rate. Basically, it is very, very hard.

I've given a very quick check at the literature and the best I've found is something like this:"The more dramatic and novel set of findings, however, was the difference in the progression of alcohol use after initiation. Once White adolescents had had a first drink, they were extremely likely (over 85% probability for most point estimates) to continue reporting alcohol use in subsequent years, regardless of age of first use. The likelihood of continued drinking for Black youth was dramatically lower, typically between 60% and 80% probability. Again, Hispanic teens showed an intermediate pattern (approximately 80–90% probability)."

I find the in class serious use of data from an obviously politically inclined source unwise from an ethical point of view. Like MelonFace wrote, every stat is theoretically possible but...

Even if the numbers tell a true story, there is a big but.

When judging the validity of statistics, you have to ask yourself what is the population they pretend to cover and what is the population they actually cover.

"For kids who start drinking...", are those kids from the family of six who live next to the producers? With any stats, if this question cannot be answered precisely, the stats have little face value.