Also, if your safety net is that big brother is going to prevent your kid from doing heroin... well... you're gonna have a bad time. Education is key. Having a good and nurturing relationship with your kid is key.
Anecdotally: there are places in the world where kids can have alcohol even as young as 10-12. Not legally, but within the family and it's not taboo for a kid to try it out if they're curios. I'm going to let you guess which places have more trouble with alcohol abuse: places where it's treated like any other thing and kids can try it or places where it's illegal to drink it until you're 18 or 21.
And given alternatives, most people probably wouldn't try it - especially given it's reputation.
You can't stop something as pervasive as drugs no matter how many people you incarcerate or kill attempting to do so. Prohibition has a real cost and it isn't low, time will tell but I am unsure why the current pohibition and its related drug cartels are viewed any differently than Al Capone and alcohol prohibiation. We can legalize it, tax it, regulate it, and further educate people to make good choices. We can eliminate drug cartels and remove funding from vast criminal networks across the US all in one go. We can train people to be nurses and mental health workers instead of cops and DEA agents. And we can probably _save_ money in the process.
Most countries do just this. Of course some will get through the cracks, but they're aiming to lower the number of users, not hit 0 exactly. Also, you don't have the data to say that making heroin and meth as available as alcohol actually works on a large scale.