Mass. Gen. Laws ch. 32 § 60
Sections fifty-six to fifty-nine, inclusive, shall, notwithstanding the provisions of any general or special law relating to retirement allowances, be in effect in any county, city, town or district which accepted them or accepted corresponding provisions of law prior to January first, nineteen hundred and forty-six, by the retiring authority.
No veteran whose employment first begins after June thirtieth, nineteen hundred and thirty-nine, shall be subject to the provisions of sections fifty-six to fifty-nine, inclusive; nor shall any veteran whose employment first began on or before said June thirtieth be subject to said provisions unless at the time of his retirement the total period of his creditable service is at least equal to twice the time he was not in the employ of the commonwealth or of a county, city, town, district, housing authority or redevelopment authority subsequent to the date when his employment by the commonwealth or by a county, city, town, district, housing authority or redevelopment authority first began.
Mass. Gen. Laws ch. 32, § 60