Indiana Code Title 25. Professions and Occupations § 25-28.5-1-19

(a) No such applicant shall be granted a license in a category he is not licensed in another state.

(b) The individual applicant for a license as a plumbing contractor or a journeyman plumber shall be at least eighteen (18) years of age.

(c) The requirements for the licensing or registration of plumbing contractors or journeyman plumbers in such other state, territory, country, or province, were, at the date of the applicant's last registration or licensing, substantially equal to the requirements in force in this state;  and:  Provided, That the same privilege of registration or licensing is accorded by said state, territory, country or province to licensees of the State of Indiana.