The Philadelphia Gas Works shall establish and maintain, until and unless terminated by ordinance, a reduction in charges for natural gas distribution and supply services for any eligible senior citizen in the amount of twenty percent (20%) of the charges for heating and non-heating purposes to his or her residence. In order to qualify for this reduction, an eligible senior citizen must first apply to the Philadelphia Gas Works for a rate reduction at least thirty days before the next scheduled meter reading. The reduction shall then take effect at the start of the succeeding billing period. Any senior citizen currently receiving a rate reduction under the terms of the 1973 Ordinance shall continue to receive the reduction without applying under the provisions of this Section.