PC 666 is what we call a wobbler which means that it can be charged either as a felony or a misdemeanor. A juvenile adjudication is not considered a crime although since your son didn't have the records sealed on reaching 18, it can be considered in charging. Your son's attorney should know the rules applicable. As PC 666 requires a prior conviction, and your son doesn't have one, I'd argue that the felony charge is wrong. In fact a misdemeanor 666 may be the wrong charge if you disregard the juvenile adjudication.