The age to get married in Massachusetts without parental consent is eighteen. See the below link for more information.
None of the information or materials posted above is intended to constitute legal advice. Viewing this does not constitute an attorney client relationship. Local counsel should always be consulted before contemplating any legal action. The above information is general in nature and should not be undertaken without the express advice of an attorney of your choosing.
You're both adults. You can do as you please. There's nothing her parents can legally do to stop you. The only legal right they have is to make sure that your girlfriend doesn't inherit anything if she does marry you by cutting her out of their wills.
While it's not a legal issue, your girlfriend needs to do some serious soul-searching about the possible long-term consequences of her actions for her relationship with her parents and other members of the family.
E. Alexandra "Sasha" Golden is a Massachusetts lawyer. All answers are based on Massachusetts law. All answers are for educational purposes and no attorney-client relationship is formed by providing an answer to a question.