Article I section 8 (powers of Congress)
To provide for calling forth the Militia to execute the Laws of the Union, suppress Insurrections and repel Invasions;
To provide for organizing, arming, and disciplining, the Militia, and for governing such Part of them as may be employed in the Service of the United States, reserving to the States respectively, the Appointment of the Officers, and the Authority of training the Militia according to the discipline prescribed by Congress;
Under this authority the Militia Act of 1903 created the Reserve Militia which consists of all able bodied men between the ages of 17 and 45; and the Organized Militia, which are all the state militias. Per RCW 38.04.030 I'm a member of the Washington State Militia even though I'm about to turn 65, Our unorganized militia has no upper age limit (and no reference to gender :) )
Edited to add: the English laws are relevant because most of the legal systems and laws set up in the colonial states were based on English law, since that's what we'd been living under.