My Dad is 77 years old and receiving social security benefits, did not file last year, how much 1099 income can he make without having to file taxes?

[MarilynG1]

As a single person over 65, he is required to file if his gross income exceeds $15,700.

Here's more info on Filing Requirements.

Whether or not his Social Security income is taxable depends on his total income, including his Social Security plus any other income.  If half of his social security income, plus other income, exceeds $25,000, part of his social security income becomes taxable.

Click this link for more details on Is My Social Security Taxable?