There is no "senior" rate for the tax. You do get a higher Standard Deduction if you are over 65. Check 1040 line 9 for it.
For 2019 the standard deduction amounts are:
Single 12,200 + 1,650 for 65 and over or blind
HOH 18,350 + 1,650for 65 and over or blind
Joint 24,400+ 1,300 for each 65 and over or blind
Married filing Separate 12,200 + 1,300 for 65 and over or blind
