R. Chaim Jachter, author of the recently published Gray Matter volume 2, wrote about why teenagers should not drink alcohol on Purim from an halakhic perspective -- how can we preach that teens ignore an explicit mitzvah? His Bikkurei Shabbos is available online here (PDF), and the discussion is on page 20. The following is my translation of it into English:
A statement was released by the OU stating that high school-aged youth should not fulfill the mitzvah of drinking [alcohol] on Purim until they "do not know." I suggested to my students that this pronouncement is based[?] on the words of the Chayei Adam, brought in the Bi'ur Halakhah (695:2 sv. ad de-lo yada): "However, one who knows that he will be brought to denigrating a mitzvah such as washing one's hands, blessings and the grace after meals, or will not pray minchah or ma'ariv, or will act foolishly -- it is better for him not to get drunk, and all his actions should be for the sake of Heaven."See here for some serious emphasis from the OU on not getting drunk on Purim.
I add that since in past years there have been accidents involving youth who are drunk on Purim, this obligation does not apply to youth. Additionally, today's psychologists state that the judgment of youth is not complete and therefore, to our dismay, we often hear of accidents involving youth. In truth, this evaluation has echoes in our [Torah] sources. The Rema (Yoreh De'ah 61:5) wrote: "Some are strict and do not give kabbalah to someone under the age of 18, because only then does the man become a bar da'as and knows how to be careful." And similarly in Shulchan Arukh (Choshen Mishpat 67:3): "Some say that it is not proper to serve as a judge until the age of 18 and above." Also, this might be what the Sages meant in Avos when they said, "The age of 18 for marriage." Before that age, one's judgment is not sufficiently complete to be able to raise a family (cf. Beis Shmuel [1:3] and Chelkas Mechokek [1:2] who ask why the mitzvah of procreation is different from other mtizvos, that it begins at the age of 18 and others at 13).
Do not ask from the fact that previous generations did not make such pronouncements, since previous generations did not have the danger that today's youth, who drive cars, have. Therefore, they would go around the neighborhoods of their parents and the parents could watch over them, which is not the case today.