(1) Minors are: (a) males under 18 years of age; (b) females under 18 years of age. (2) All other persons are adults.
Mont. Code Ann. § 41-1-101, under Minority.
Mont. Code Ann. § 41-1-101
(1) Minors are: (a) males under 18 years of age; (b) females under 18 years of age. (2) All other persons are adults.