Medigap Plan A is the supplement available to people under 65 in some states as long as you qualify for Medicare early because of a disability. It is made available for purchase during your open enrollment period without any underwriting.
However, the cost for this plan for people under 65 can be much higher than what a 65-year-old will pay. This is because people who qualify for Medicare due to a disability oftentimes have higher medical costs.
Because of this, it may make more sense for those who are eligible for Medicare because of a disability may be better served by a Medicare Advantage plan. Medicare Advantage plans offer the same rate for anyone regardless of age, gender, or even disability.