Article 66 of the 1964 Constitution of Zambia states: "Every citizen of Zambia who has attained the age of eighteen years shall, unless he is disqualified by Parliament from registration as a voter for the purposes of elections to the National Assembly, be entitled to be registered as such a voter under a law in that behalf, and no other person may be so registered."

Article 75, clause 1 of the 1991 Constitution grants every citizen of Zambia who has attained the age of eighteen years is entitled to be registered as a voter (Election Access, "Zambia").

https://www.worldstatesmen.org/Constitution-Zambia1964.pdf