Your credit score doesn't know you retired. It doesn't care about your income — remember, income isn't part of the credit score calculation. What changes is your ability to handle financial shocks.
Your credit score stays the same. Retiring doesn't lower your score. If you have good credit at 64, you'll have good credit at 65. As long as you keep paying on time and don't rack up debt, your score is fine.
But your buffer shrinks. When you were working, an unexpected $5,000 bill was uncomfortable but manageable — you could absorb it over a few paychecks. On a pension, that same $5,000 might mean choosing between credit card debt and medication.
Insurance matters more. Car insurance and homeowner's insurance companies check credit. A good credit score keeps your premiums lower. Protecting your credit directly saves you money on insurance.
When your credit score stops mattering: If you own your home outright, drive a paid-off car, aren't cosigning anyone else's loans, and aren't applying for new credit, your credit score is essentially irrelevant. Some people in this position reasonably decide not to worry about it.
But don't let it collapse intentionally. Even if you don't "need" credit, you can't predict the future. A medical emergency, a move to a new rental, or an unexpected major expense could require access to credit. Keep your credit healthy as insurance against the unknown.