(a) Different age and residence requirements from those prescribed by Section 141.001 may be prescribed by a home-rule city charter, but a minimum age may not be more than 21 years and a minimum length of residence in the state or city may not be more than 12 months immediately preceding election day.
(b) A charter provision is void if it prescribes a minimum age requirement of more than 21 years or a minimum length of residence requirement of more than 12 months.