If I retained my insurance, due to ACA look back period, when I retired at 65, will I be I be penalized if I do not enroll in Medicare now?

Let me try to explain a little better. I retired from a large hospital on Feb 4th this year but I remained employed in an as needed capacity. The ACA look back showed that I worked at least 30 hours a week last year. Because I worked at least 30 hours a week last year and I remained employed in the as needed capacity after I retired, I was eligible to keep my health insurance for remainder of this year at the same premium I was paying when full time. While I am no longer a full time employee I am still employed there and I do work there an average of 1 to 2 days per week. In this situation and with this health insurance coverage, will I be penalized if I delay signing up for Medicare part B and D until the next open enrollment in January 2018?

Yes.   You must enroll when you become eligible or pay.

You have only 3 months...including the month you turn 65 to do this. After that, you will pay the higher premium for the rest of your life. Just how high? Depends on how long you wait.

Go to the Medicare.gov website...there you can see the calculations.

As for ACA look back?   What?   The only "look back" I have ever heard of is that you must have some insurance each year to avoid the penality.    But...once you change over to Medicare, ,you coverage would be continuous...you drop one when you start the next.    All of which is permissible because of a "life changing event".