Altering, from 55 years old to 50 years old, the age at which a resident is eligible for a subtraction modification under the Maryland income tax for retirement income attributable to employment as a correctional officer, law enforcement officer, or fire, rescue or emergency services personnel in the United State, the State or a political subdivision of the State; altering the amount of certain retirement income that may be included under a certain subtraction modification; applying the Act to certain taxable years; etc.