Keeping it illegal does not make it less accessible to youths. I would argue it goes the other way. Street dealers don't take ID, they don't care how old you are. If you legalize it and make it available in stores to people over a certain age (likely 18, maybe 21 if you really want to try your best to keep it out of high schools), it will be more difficult for those underage to get it, unless they pay an older friend to do it, or find a black market for it (which will likely still exist, but hopefully on a much smaller, less accessible, scale). This is no different than alcohol is now.
In my experience, unless you were able to steal it from your parents, getting booze as an under-ager was more difficult than pot. All you had to do was go to a stoner friend and they would either sell you some or give you their guy.
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