Unable to check box in Turbotax on Maryland Form 502R, Part 3

It depends. If you are below retirement age and you are permanently disabled you will be asked a question in the Maryland (MD) return.

When you complete your 1099-R in the federal return, Box 7 should have a code 3, which indicates disability.  You will be asked questions about your retirement so it's important to answer them correctly as you enter the income.  Go back to your 1099-R to review.

Once you get to the MD return you should be asked 'Let's Double Check Disability Status' where you can check you are totally disabled.  

If you are at or over the minimum retirement age, then you will see this screen in TurboTax and that will prompt part one of the Pension Exclusion Computation Worksheet to be populated, which will give you the pension exclusion in MD. See the MD image below showing this question.