Any person who is at least 55 years of age and who has been an employee of said house of correction for a period of 10 years or more and has contributed to said fund for a period of not less than the full term of service, or shall pay into the fund the amount of money such person would have paid had contributions been made by him at the prevailing rate from the first day of his employment, together with interest at 4% on each such contribution from the time it should have been paid until it was paid, may retire from the service of said house of correction upon 60 days notice, to be given to said board of trustees (unless such notice is waived by said board of trustees) and become an annuitant under this Division.
40 ILCS 5/19-111