Mass. Gen. Laws ch. 33, § 2: Membership

Section 2. The militia of the commonwealth shall consist of: (i) all able-bodied citizens and all other able-bodied persons who have declared their intention to become citizens of the United States, between the ages of 18 and 65, and who are residents of the commonwealth; and (ii) such other persons who, upon their own application, enlist or are commissioned pursuant to this chapter, subject to exemptions created by law.