There is no senior discount on the price of TurboTax. Are you looking for the deduction for seniors on your federal tax return?
You don't have to enter anything to get the deduction for seniors. TurboTax will give it to you automatically based on the birth date that you entered in your personal information, and your income.
The deduction for seniors is calculated in Part V of Schedule 1-A. The amount of the deduction will be on Schedule 1-A line 37. The total deductions from Schedule 1-A will be on Form 1040 line 13b, which might include other deductions besides the deduction for seniors.