Getting carded (for drinking) is very rare in Japan, in fact I have never seen it happen when out with student groups.

With that said though it's always good to "follow the laws" of the host nation even if there is no chance you'll get caught or not. At least that's how I operate, but I'm a goodie two shoes.

But you shouldn't have any problems if you wanted.

Getting carded to enter clubs is another story (at least in Shibuya), everyone was carded at the places I went to.

Of course I have no problems, I was 20 years old ages ago...@_@