Can I still file back years tax returns from 2014 2015 and 2016

"Can I still file back years tax returns from 2014 2015 and 2016"

You can do so, but TurboTax products for previous years only go back to 2016.

See https://turbotax.intuit.com/personal-taxes/past-years-products/

If you only get ssi or SS or SSDI  it is not taxable and you do not have to file a return.  And there is no benefit in claiming dependents or deductions.   Unless you have federal income taxes withheld from the benefits or you get health care insurance through one of the state marketplace exchanges and receive a Form 1095-A then you need to file a tax return.

If you need to file i have links to the blank IRS forms for the years.  Like here are some blank forms & instructions for 2014

1040 https://www.irs.gov/pub/irs-prior/f1040--2014.pdf     

Instructions https://www.irs.gov/pub/irs-prior/i1040gi--2014.pdf

1040A https://www.irs.gov/pub/irs-prior/f1040a--2014.pdf    

Instructions https://www.irs.gov/pub/irs-prior/i1040a--2014.pdf

1040EZ https://www.irs.gov/pub/irs-prior/f1040ez--2014.pdf    

Instructions https://www.irs.gov/pub/irs-prior/i1040ez--2014.pdf

2014 Tax Tables https://www.irs.gov/pub/irs-prior/i1040tt--2014.pdf

Publication 17 Tax Guide for 2014 https://www.irs.gov/pub/irs-prior/p17--2014.pdf

It's too late to get a refund for 2016 or earlier. You can file the tax returns, but if they show a refund you will not get the refund. If they show a payment due, you still have to pay it.