C.R.S. § 18-12-112.5

(1) (a) It is unlawful for a licensed gun dealer to transfer a firearm to a transferee until the dealer has obtained approval for the firearms transfer from the bureau after the bureau has completed any background check required by state or federal law.

(a.3) A person who is a licensed gun dealer shall not make or facilitate the sale of a firearm to a person who is less than twenty-one years of age.

(a.5) It is unlawful for a person who is less than twenty-one years of age to purchase a firearm. This subsection (1)(a.5) and subsection (1)(a.3) of this section do not apply if:

(I) The person is an active member of the United States armed forces while on duty and serving in conformance with the policies of the United States armed forces; or

(II) The person is a peace officer, as described in section 16-2.5-101, while on duty and serving in conformance with the policies of the employing agency, as set forth in section 16-2.5-101 and section 16-2.5-135; or

(III) An individual certified by the P.O.S.T. board pursuant to section 16-2.5-102.

(b) Transferring or selling a firearm in violation of this subsection (1) is a class 1 misdemeanor.

(c) Purchasing a firearm in violation of this subsection (1) is a class 2 misdemeanor.

(2) This section does not apply to the sale of an antique firearm, as defined in 18 U.S.C. sec. 921 (a)(16), as amended, or a curio or relic, as defined in 27 CFR 478.11, as amended.

(3) As used in this section, unless the context otherwise requires:

(a) "Licensed gun dealer" has the same meaning set forth in section 18-12-506.

(b) "Transfer" has the same meaning set forth in section 24-33.5-424.