Each optional form of allowance shall be the actuarial equivalent of the basic allowance under the State system of a member. Subject to paragraph (2) of this subsection, for an optional form of allowance providing for payment to a designated beneficiary for life, the designated beneficiary must be an individual. If the designated beneficiary is a minor or an individual with a disability, the allowance may be paid into a trust for the benefit of the individual. A member who elects to receive a reduced optional allowance under § 21-403 of this subtitle may designate an individual other than the member’s child as the member’s designated beneficiary. This subsection applies to a member who selects an optional form of allowance as provided in § 21-403(b) or (e) of this subtitle. If a member designates a beneficiary other than the member’s spouse or disabled child as defined under § 72(m)(7) of the Internal Revenue Code, a member may not designate a beneficiary who is more than 10 years younger than the member.