Do my parent need to start filing tax returns again?

My parents are in their 80's. Because of their low income, they haven't had to file taxes since 2010. Apparently the tax person they previously used said they didn't need to file a return? 

In 2017 my parents inherited mutual funds and stock that have paid dividends. I ran the numbers with TurboTax and their returns showed owing zero to both the Federal and State of Ohio. My question is should they start filing tax returns again?