https://www.medicare.gov/basics/get-started-with-medicare/sign-up/when-does-medicare-coverage-start
Signing up for Premium-free Part A later
You can sign up for Part A any time after you turn 65. Your Part A coverage starts 6 months back from when you sign up or when you apply for benefits from Social Security (or the Railroad Retirement Board). Coverage can’t start earlier than the month you turned 65.
