attempting to deny drugs (via prohibition) does not keep them from being used, and it has not done anything for usage rates. A properly implemented legalization is not giving up it is changing tactics.
Getting back to the availability of alcohol versus marijuana these stats are from the NIDA here is the link:
High School and Youth Trends | DrugFacts | National Institute on Drug Abuse
this is a comparison of alcohol and marijuana usage rates by grade in school children (within the last month):
So tell me, how effective is this drug war in keeping drugs from our kids, and how effective is it at delaying the age of first use? it seems that the majority of kids start on marijuana - the prohibited and supposedly least available option MUCH earlier then the prevalent and supposedly more available alcohol. Kids use marijuana more frequently at younger ages then they do alcohol. The stats do not support what you are trying to argue. If we legalize it and control it we can -say it with me now - "DELAY THE AGE OF FIRST USE" - and this is critical for a long term and overall drug strategy of minimizing addiction rates, usage rates, and the associated harms that may occur as a result.