(a) Each member employer that has adopted a plan for the provision of retirement benefits or employee benefits under Code Section 47-5-40 is authorized in its plan and contract to include such provisions as are necessary for the development of a suitable plan, which provisions shall be subject to the approval of the board of trustees, including, but not limited to, the following:

(1) Minimum age at entry into its plan;

(2) Minimum years of service at entry into its plan;

(3) Maximum years of service credit allowable;

(4) Provisions relating to separation and return to employment;

(5) Types of benefits to be provided;

(6) Types of vesting provisions, if any, to be provided;

(7) Types of disability retirement provisions, if any, to be provided;

(8) Minimum years of required participation in the plan;

(9) Provisions relating to benefits for part-time employment; and

(10) Any other provisions necessary, incidental, or helpful in providing the intended benefits.

(b) The board of trustees is authorized to reject any contract provision which it determines to be actuarially unsound or which it determines would create an undue administrative burden.