Up to 85% of your Social Security benefits can be taxable on your federal tax return. There is no age limit for having to pay taxes on Social Security benefits if you have other sources of income along with the SS benefits. When you have other income such as earnings from continuing to work, investment income, pensions, etc. up to 85% of your SS can be taxable.
To see how much of your Social Security was taxable, look at line 14b of your 1040A, or line 20b of your 1040
https://ttlc.intuit.com/questions/1899144-is-my-social-security-income-taxable