During the Artie segment, some of the glee members a year older than him are still students, and some have graduated.
It's a myth that Jews cannot get tattoos.
Puck's long-established devotion to Judaism would have prevented him from getting a tattoo due to the religious proscription against intentional defacement of one's body.
After Artie's dream, he bends his knees slightly so Finn can pick him up.