Most Senators are already eligible for retirement.
Eligibility is based on a Senator’s age and years of service. Senators age 50 and over need 12 years of service to retire. Senators age 60 and older need 8 years of service to retire.
Retirement is a factor that Senators consider when deciding whether to run for reelection. A senator that is already eligible is not motivated by retirement. Conversely, senators who are not eligible have additional incentive to seek reelection.