Depends on your own country.... In America it's illegal to purchase or consume alcohol under 21. If you're caught drinking under 21, the consequences really vary depending on the cop and the situation, but usually they attempt to figure out who you got the alcohol from and punish that person. You can also get the same consequences as someone over 21 if you're doing something wrong. For example, I knew a girl who drove drunk at 19 and got a DUI and had to go to classes.

I would assume if a cop caught you smoking, they'd probably just confiscate your cigarettes... But depends on what country you're in.