Yes, you can file 2017 (I think... I don't remember any of the extenders impacting 2017).

Efile reopened today 1.27.20.  Generally, when efile is open, one can file the current year plus two prior years.  Unfortunately, due to Congress passing extenders retroactively, 2018 returns can't be efiled until the IRS can get the 2018 forms revised.