are you claiming him and receiving the 'other dependent tax credit? (which you may be able to if he still living at home - run through TT and see what TT advices you to do.
The reason for asking is the answer is different whether or not you claim him as a dependent
see link below and especially the sub-heading 'dependent tax filing'
https://turbotax.intuit.com/tax-tips/irs-tax-return/does-everyone-need-to-file-an-income-tax-return/...
if your son uses TT, TT will figure out whether filing is necessary or not, but it begins with whether you are declaring him as a dependent or not on your return
