Eighteen
http://www.in.gov/isp/files/firearms_FAQ_02_08.pdf
Who may not be eligible for a license to carry?
IC 35-47-2-3
(g) A license to carry a handgun shall not be issued to any person who:
(1) has been convicted of a felony;
(2) has had a license to carry a handgun suspended, unless the person's license
has been reinstated;
(3)
is under eighteen (18) years of age;
(4) is under twenty-three (23) years of age if the person has been adjudicated a
delinquent child for an act that would be a felony if committed by an adult; or
(5) has been arrested for a Class A or Class B felony, or any other felony that was
committed while armed with a deadly weapon or that involved the use of violence, if a
court has found probable cause to believe that the person committed the offense
charged.
In the case of an arrest under subdivision (5), a license to carry a handgun may be
issued to a person who has been acquitted of the specific offense charged or if the
charges for the specific offense are dismissed.