An underage performer in mainstream porn is almost unthinkable these days. Producers have to carefully document the age of their performers. Back in the day porn producers paid protection money to the mob, who in turn paid off law enforcement (there is an oral history of porn where some people are really pissed off about John Gotti ordering Robert "DB" DiBernardo - who controlled the porn business for the Gambinos - to be killed; they actually missed that guy). Even so, by the time Traci Lords was eighteen and had left the porn business, the police were looking for her (while she was on the set of John Waters' Cry-Baby.
Speaking of the mob, in the 1970s Roy Demeo was allegedly involved in the production of child pornography, angering both his skipper Nino Gaggi and Gambino boss Paul Castellano (who nevertheless gladly took their cut of the money).