For the purpose of this section, when an employee shall have attained the age of eighteen years the said employee may be eligible to participate in the defined group plans.

A county board of education, the Teachers' Retirement Board, the West Virginia Board of Education and the board of regents of West Virginia and their agencies may provide by written agreement between any such board or agency and any teacher or other employee to reduce the cash salary payable to such teacher or other employee, and, in consideration thereof, to pay an amount equal to the amount of such reduction as premiums on an annuity contract or payments on a custodial account or other investment owned by such teacher or other employee, which annuity contract, custodial account or other investment is in such form and upon such terms as will qualify the payments thereon for tax deferment under the United States Internal Revenue Code. The amount of such reduction shall not exceed the amount excludable from income under section 403(b) of the United States Internal Revenue Code, and amendments and successor provisions thereto, and shall be considered a part of the teacher's or employee's salary for all purposes other than federal and state income tax.

The purchase of such tax deferred investment for a teacher or other employee by a Board of Education, the Teachers' Retirement Board, the West Virginia Board of Education and the board of regents of West Virginia and their agencies shall impose no liability nor responsibility whatsoever on said boards or members thereof except to show that the payments have been remitted for the purposes for which deducted.