Your first chance to enroll in Medicare is around age 65 when you have a seven-month window to apply. This is your Medicare Initial Enrollment Period. You can file for Original Medicare Parts A and B, or sign up for a private Medicare plan at any time during the three months before, the month of, and the three months after your 65th birthday.
Need coverage the month you turn 65? You should sign up in the three-month window before your birthday.