Every teacher who has annually contributed to the fund in accordance with this part for at least five (5) years and has taught in the public schools not less than twenty-five (25) years, fifteen (15) years of which have been in the public schools of a city, town, county or district, may be retired by the board of education, and shall have the right to voluntarily retire from such service and become the beneficiary of this part. Every such teacher so retiring or retired shall be entitled to an annuity for the remainder of the teacher's life, to be paid out of the fund, an amount as provided by §49-5-904.