The age deduction (age amount) is
calculated automatically if you eligible for it. You are eligible for this
amount if you were 65 years of age or older on December 31, 2017, and your net
income (line 236 of your return) is less than $84,597. If you were an immigrant
or emigrant, your claim is prorated for the time you were resident in Canada.
More information on the age
amount: https://turbotax.intuit.ca/tips/claiming-the-age-amount-tax-deduction-5568
