Try and do a search here, even though the search function sucks. It has been discussed many times.

He's still renting it, right, your question isn't about selling it?  Lots of questions and answers here about what to do at sale, but if it's still a rental just do the current year correctly and worry about catching up if the property is ever sold.  October 15 is less than a week away.  Unless someone wants to chime in with a way to catch up on missing years, this year.  

Check instructions for form 3115

Did not claim "in many prior years" or did not claim EVER?

You need to find out if it was claimed in the first and/or second year it was placed in service.  That is what determines what needs to be done.

One put into rental in 2007 and another in 2017, depreciation was never claimed, and no Form 4562 was ever filed with IRS. If I claim depreciation just this year, Form 4562 is not printed.