I suppose it’s not as bad as it sounds because the RMD would be less than 1.5% of the balance for most years. And he should be able to convince IRS to waive the penalty. Have returns been filed for him, because of other income? Otherwise, the 5329 is a stand-alone return, there is no statute of limitations if no return was filed in the first place. File one for every year, but the waiver explanation can be the same.

I hope you aren’t also doing returns for the parent or conservator who is responsible for the mistake, or the Commission-Filled Pockets guy who is a tax law expert also, unless they have agreed to pay any penalties that are assessed.