Sec. 5.05. EARLY RETIREMENT. (a) A member is eligible to retire and receive a normal service retirement annuity if the member, while serving as a firefighter in the fire department:

(1) has attained the age of 45 years and has at least 10 years of service credit in the fund; or

(2) has at least 20 years of service credit, regardless of age.

(b) The retirement annuity of a person who retires under this section after September 1, 1997, is the same as for normal service retirement, but may not be increased under Section 9.04 of this Act until the person would have met the requirements of Section 5.01 of this Act if the person had remained in active service as a firefighter.