It seems unlikely that this is an IRA, but is instead a 401(k) or similar employer plan. There is no 20% mandatory withholding requirement for distributions from an IRA and no age-55 penalty exception for distributions from an IRA. If this was not an IRA, the IRA/SEP/SIMPLE box will not have been marked on the Form 1099-R provided by the payer. The payer also would normally know that your distribution from a 401(k) or similar plan qualified for the age-55 penalty exception and would have used code 2 in box 7 of the Form 1099-R to indicate that there is no penalty.
