I don't know how this could be any more clear. This is the language from the statute that was passed:
Summary of Public Law 2015, Chapter 327 (127th Legis., LD 652)
Summary of Public Law 2015, Chapter 327 (127th Legis., LD 652)
Concealed carry without a permit is limited to people who are 21 or older,
with the following exception: If a person is 18 years of age or older, and is
on active duty in the Armed Forces of the United States or the National
Guard, or has been honorably discharged from the Armed Forces or the
National Guard, and is not otherwise prohibited from carrying a firearm, the
person may carry a concealed handgun. A person who is 18-20 years old
and without the referenced military qualifications must have a permit to
carry concealed. The law applies to both residents of Maine and nonresidents.