Justin Bieber broke out his finest party tank top and hit the NYC club scene HARD last night -- rollin' to 3 hot spots in a matter of hours ... problem is, he's not 21.
Cameras rolled as Bieber and his posse rolled into Avenue nightclub (where Lindsay Lohan allegedly punched a gypsy) ... then to Marquee ... followed by 1 Oak.
Here's the issue ... we checked into the age requirements to hit the different venues and we found Marquee had advertised that Wednesday was a 21+ night.
Bieber is only 19.
It's possible Marquee has a license to allow minors into the venue ... and they CHOSE to make it a 21+ night, which would mean no laws were broken. We're checking into that ...
Ditto for Avenue ... which also advertised Wednesday as a 21+ evening.
As for 1 Oak -- we're diggin' on that.
We called and emailed Marquee & Avenue & 1 Oak for comment -- so far, no word back.