My relative is a permanent resident/green card holder in the US - not a citizen. The person worked and paid federal taxes in the US for ~30 years. (I don't quite understand why they didn't seek citizenship.)
Are they entitled to social security retirement benefits? Can they start to receive early retirement benefits at age 62?
Is there any distinction between a green card holder and a citizen in terms of social security retirement benefits, everything else being equal?
To see what they are qualified for based on their actual contributions they need to create an account at https://www.ssa.gov/myaccount/. This US government account uses their actual social security record for earnings and taxes and calculates what they are qualified for.
It is good for everybody to do this so that they can see what they qualify for and to correct any mistakes.
Yes, they qualify for Social Security benefits, and yes, they can apply for Social Security benefits at age 62. Whether it is a wise financial decision to apply for SS benefits at age 62 or to wait till later is a separate issue whose answer depends on lots of other facts that the OP has not revealed. If the recipient is in poor health and not likely to live long or needs the money to meet current living expenses (e.g. because the person is no longer working and getting a salary/wages), then starting SS benefits at age 62 is a good idea. For a person in good health and not needing the SS benefit money to live on, postponing taking the SS benefits to a later age results in a larger monthly benefit, and more likely a larger total benefit.