Eligibility for Social Security depends on your social security retirement age.
The earlier you apply for payments, the more your payment is reduced for the rest of your life. I think everyone knows that, but you do need to think about your possible life expectancy as that higher Social Security payment might really help in the future.
Of course, if you need Social Security Disability payments, an early payment to begin at any age, if you are unable to work due to an illness or injury, then the following Social Security ages don't apply.
The Social Security Survivor Benefit can begin at age 60, if your spouse dies an early death.
The Social Security Early Retirement benefit starts at age 62. This is a reduced benefit payment, when someone wants to retire early.
Until a few years ago, Age 65 was the "full retirement age" and where you no longer had a Social Security income limit.
Age 65 is also when you are eligible for Medicare too.
Depending on your birth date, your full retirement age (meaning a full benefit payment too). For example, If you were born between 1943 and 1954, your full retirement age is 66.
I was born in 1955, my full retirement age is 66 years and 3 months... if I wait.
Assuming you continue to work after your full retirement age, you can "double dip"... working AND collecting Social Security payments too. You too can "double dip". Read more here... my argument for working longer...
Finally, if you did apply early, you can always look at a Social Security Early Retirement recalculation -- it happens!