Massachusetts General Laws Part I. Administration of the Government (Ch. 1-182) Ch. 51, § 47A

If, after examination of an affidavit of registration, it appears to the registrars that the person has all the qualifications to be registered as a voter except that of age and the person has obtained the age of 16, then they shall enter the person's name in the current annual register of voters with the designation “pre-registrant” or other term or code as specified by the state secretary. The designation shall be removed when the person, on or before the day of the next preliminary, primary, special or general election or town meeting, attains full age. No pre-registrant shall be allowed to vote until the pre-registrant obtains full age unless otherwise permitted by law.