You could use the Visitor Controller by TwoJeffs to ban kids and teens from nightclub/bar lots. It is available here:
http://www.simbology.com/smf/index.php?topic=17.0Or on lots where you would want teens, like a dance club, remove the bar area and make something else like a snack area with vending machines and a few tables and chairs.
Or it might be possible to use SimPE to alter a cloned bar - changing the flags to disable it for teens. You might have to look up a tutorial because I'm not quite sure how to do it. Mod the Sims has some bars you can download if you want to try.
They are only supposed to serve juice, which is why teens can use them but they do look like real bars so I can see the problem. Good luck!