An initial enrollment period is a period where you are immune to medical underwriting. This means if you had a surgery that would prevent you from enrolling into a supplement plan it doesn’t count against you during this period. If you can pay for one of these medicare supplement plans you can get on them so long as you maintain your payments.
Your initial enrollment period starts 3 months before your 65th birthday month and ends 3 months after. It lasts a total of 7 months. During that time you can switch to any plan you want to!