Answer:
(This is for Pennsylvania; all states are different.)
General requirements: The Pennsylvania Constitution states, and I quote, "Senators shall be at least twenty-five years of age and Representatives twenty-one years of age. They shall have been citizens and inhabitants of their respective districts one year next before their election (unless absent on the public business of the United States or of this State) and shall reside in their respective districts during their terms of service."
Term in office: 6-year terms
Salary: $174,000 per annum