This is a long-standing defect in the Step-by-Step interview in TurboTax. The question about your RMD is in the 1099-R section of the interview. Since you didn't take any distribution at all, you have no Form 1099-R to enter, so you never get the question.
Since you are using the CD/Download TurboTax software, you can easily make the necessary entries on Form 5329 in forms mode to show that you did not take the RMD and to request a waiver of the penalty. Switch to forms mode, click the Open Form icon at the top left, and open Form 5329. (There are two copies of Form 5329. Form 5329-T is for the taxpayer, and 5329-S is for the spouse on a joint return.) You only have to fill out Part IX, which is the last section all the way at the end of the form. Enter the RMD amount that you should have taken in 2018 on line 52 and zero on line 53. Between lines 53 and 54 there is a box where you can enter the amount you are requesting a waiver for, which would be the same amount that you entered on line 52. TurboTax will make the necessary entries on lines 54 and 55. Then click the Explain button to open the Explanation Statement form and enter your explanation. In your explanation statement, briefly state the reason you did not take the RMD, to show that it was "due to reasonable error," and state that you have rectified the error by taking the distribution in early 2019.
The Form 5329 and the explanation statement will be included in your tax return. TurboTax will not include Schedule 4 in your tax return (unless, of course, you have some other entry on Schedule 4). I don't think you need Schedule 4 because it will just have zero for the penalty.
