Hi Richard,
IRA accounts subject to a "5-year hold" are generally Roth IRA accounts. For the distribution of gains from a Roth IRA to be tax-free, the source funds must have been held in a Roth IRA for at least 5 years, and the account holder must be at least 59 1/2 years old when the distribution occurs.
The IRMAA, or the Income-Related Monthly Adjustment Amount, is a Social Security item related to Medicare. Unfortunately, this is not a tax-related item/calculation, so we cannot advise on how to determine this number. It would be best to contact the Social Security Administration to discuss how this is calculated for you.