Retirement tax questions

I followed instructions provided by "ANSWER" below... and tax return now shows I should receive total amount of taxes withheld in 2016 as a refund... I'm afraid there might be some kind of error on my part?

Is it likely/possible my refund is because of my age (will be 65 on 05/28/2017) and because I have been on Federal Social Security Disability Retirement for over 20 years?

A review or response would be greatly appreciated... I can't afford to make an error.

Many thanks for your assistance.