Can a senior citizen who pays for a home care aid write off any of this on a tax return?

I'd check with a CPA. It would depend on the type of home care, I assume, and if it's prescribed by a doctor. A tax expert should be able to advise you, as these things change each year. I hope you can, but I'm afraid not. However, I am not qualified to tell you. It may even make a difference where you live, so please get tax advice from someone certified.
Good luck,
Carol

You can deduct as medical expenses the cost of nursing services provided at home. But you can’t deduct the cost of personal or household services provided, such as cooking, cleaning and such. If the senior qualifies as “ chronically ill”, the costs of maintenance and personal care services are deductible too. See IRS publication 502- Medical and Dental Expenses, for more details.

It depends on what they do. If they help with a shower yes. But if they do the grocery shopping, no. You need to get you doctor to write a letter stating that they can't do certain thing for medical reasons such as limited mobility. They have to have two reasons on a list of possibilities. It is worth talking to an accountant about it.

Check with CPA, but if Doctor ordered, if person requires assistance with 2 or 3 "Activities of Daily Living", you can possibly write off cost. Depending if they are paid "W-2 payroll" or "independent contractor" - there are several ways to deduct cost of care. Inquire with CPA about "companion sitter" status for someone with dementia.

Yes. I have had home health aides for my husband who is totally disabled by a neurodegenerative illness for several years - I do deduct the enormous expenses. My husband needs help with all ADLs.