beer, wine, sparkling wine (or mixtures containing them): 16 years; 14 years if accompanied by a parent / legal guardian.
anything stronger: 18 years. The law adds: ...unless it's contained in negligible amounts; I guess this refers to, say, putting a spoonful of rum in a pound of gingerbread dough. You can't buy chocolates with liquor filling if you're under 18.
Because it's singular. "Die Jungen" = "the boys" (plural).
If it was only one boy, it'd be, "Der Junge trinkt meinen Wein."
The pronunciation of "trinken" here sounds very close to "trinkt" (actually more like "trink" to my ears). This sound file may be a bit confusing for beginners although the grammar should clearly be "trinken".
after writing the few words of the sentence my last word suggestion from was 'wife' instead of wine .. the boys drink my wife(wine)
i feel like "youths" should be accepted in place of "boys". but, what do i know. : )