From IRS Pub 17:
Single dependents—Were you either age 65 or older or blind?
No. You must file a return if any of the following apply.
• Your unearned income was more than $1,100.
• Your earned income was more than $12,400.
• Your gross income was more than the larger of:
• $1,100, or
• Your earned income (up to $12,050) plus $350
