As the other answer states, parental consent is demanded first. But, if the artist doesn't look at the form or care about age, then they could get fined a different amount depending on if they knew the person was underage or not. The one with the tattoo would not legally be able to go to jail. You cannot go to jail if you are under 18, you go to juvie. I doubt that they would get fined or go to juvie, maybe. It would be more of the artist's fault because they went against the rules of tattoo artistry.