Father has not paid taxes in several years. Is there anything I can do for him?

It well may be that your father did not have to file taxes. My brother didn't have to for many years. But only someone getting all the financial information together at end of year can tell whether income falls below the amount required for filing taxes. You should yes, see a CPA if Dad hasn't filed for years, and discuss this with a CPA, taking whatever information you have, Dad's SS income, Dad's other assets which may be getting earnings each year (which is income).
Without any change in a home it should not impact taxes very much at all other than writeoffs for repairs on any income property, and whatever.
You should also make certain Dad has a will stipulating he is leaving his home to his son, with an executor appointed, and I would see an elder law attorney (Dad's assets pay if you are POA) to see about giving home to disabled child, as this prevents some medicaid clawback often enough.
So basically you are looking at questions that need answers of experts in the field.

He is paying privately?

He may have been told by IRS he no longer had to file. Taxes are based on yearly income not what he has stashed away unless he gets a lot of interest on his savings.

My Mom and MIL, both widows, with their SS and small pension didn't bring in much more than 20k a year each. They paid no taxes because most of their income was Social Security and SS is not taxable unless you have other income and that income has to go over a certain threshold before u need to pay taxes.

If your disabled son is on Social Security Disability with Medicare and Medicaid, your Dad giving him any money will effect his benefits. Maybe not SSD and Medicare but could effect his Medicaid. I had to put my nephews money he received from his Moms insurance into a Special Needs Trust before I could get him help. I would check this out before I allowed Dad to give him money.

The next would be if Dad will need Medicaid to pay for his care in the next 5 years. In that time he can not give any of his money away. It needs to be used for his care. The house is an exempt asset but his SS and any pension he receives will be used to offset the cost of his care with Medicaid paying their share. So, might as well sell the house for his care if no one is willing to pay taxes, utilities and upkeep. And it has to sell for Market Value. And if not sold, when Dad passes a Medicaid lean will be placed on the house. Then the house will need to be sold to satisfy the lean. There are rules concerning someone living in the house or renting the house.

You can get him an accountant to go through his back taxes, and a trust and estates attorney who can get his affairs in order for the future. He should pay for both but you can gather the paperwork.

I would go to the IRS website and see what the requirements are for seniors filing tax returns.

My dad did not have to file returns based on his SS and some interest earned on a property that he sold on terms. He didn't earn enough to make his SS taxable. This was determined through a CPA. I recommend that you check IRS.gov and then speak with a tax professional to make sure you understand what needs to be done. Especially if you are looking for an inheritance, you want to know what he needs to do but, if he is on Medicaid they should be paid back from his assets before he leaves anything to his children.

Obviously a child born with disabilities is an entirely different issue and I would assume that provisions were made many years ago.

I am making the assumption you are talking about filing income taxes. I have volunteered for 11 years for TCE. We do seniors taxes for free. Many seniors have no need to file and your Dad may have been in that situation. As previously stated SS isn’t taxable if other income is low enough. The person doing his taxes would have looked at any additional income he has from pension, IRAs, interest and Dividends. Usually if no tax has been withheld from any of those items and his income from them is low enough he indeed wouldn’t have a need to file. In NY home owners have a discount program for school tax on property called senior star. I often have people file their taxes as a proof of income for their star eligibility. These taxes aren’t actually filed, just the paperwork is filled out for any senior that wants or needs it.

If your income is below $25,000 you MIGHT not be obligated to file income taxes. I was POA for my mother and did not have to file her returns for that reason. When we sold her house she did not have to pay capital gains tax because they had owned the house for 50 years.

I suggest you speak to an attorney about your father's exact circumstances, as well as for state and local rules.

Figure out if he needed to pay them, if so, file them and do an Offer in Compromise.

My FIL was 91 when he lost his wife and my husband and his oldest sister took over the money management of his household before he eventually moved to a LTC facility. He and his wife both had not filed taxes for years, either. It seems that they may have not earned enough off the small pensions they each got, but we asked our accountant about it and his answer was that he could review everything BUT said that if he found that he should, indeed, have been filing but hadn't, any new filed income tax would almost definitely trigger an IRS audit. At 92, with no assets or savings and just enough to pay for his independent living arrangement each month, we decided not to pursue it because upon reviewing his small pension it was less than the standard deduction allowed by the IRS.

From the TurboTax website regarding Seniors filing a tax return:

"For tax year 2020, you will need to file a return if:

-you are unmarried,
-at least 65 years of age, and
-your gross income is $14,050 or more

However, if you live on Social Security benefits alone, you don't include this in gross income. If this is the only income you receive, then your gross income equals zero, and you don't have to file a federal income tax return."

Consult a CPA about filing your dad's back taxes.

The IRS always gets its pound of flesh, and you have to file an estate tax return after he passes, so you might as well get this cleaned up while he's still here.

Ricky, you might want to research and then consider consulting an IRS Enrolled Agent in lieu of a CPA.   The Enrolled Agents are specifically qualified to represent people before the IRS, so their knowledge of IRS criteria, etc. is more specific.