Can I write off senior discounts if I offer them to my customers?

and you cannot use TT Free for business or self-employment income.

No you don't write them off ... you will just have less income to report.

Thanks. I will pay for it then.

There is one way you can write it off.  If you entered the full amount before the discount as income, then you can deduct the discount under Advertising or Misc Expense.

Yes, depending on your accounting methods, if it is easier to report the full price then take off the discount as an expense of some kind then that is allowed.

No.  You simply have less income to report and pay taxes on because you are selling at a lower price.  It's not an additional deduction or expense.  Just less income.