The reason for asking this question was that maybe it's possible to deduce something about such CEO. As he is not even using a calendar or mobile app to schedul

The reason for asking this question was that maybe it's possible to deduce something about such CEO. As he is not even using a calendar or mobile app to schedule his tasks upfront of at least a week, they want an assistant to remind him of everything. It seems for me that if they want someone to totally manage his time, it by default may not be 100% effective if the person didn't make a conscious action to put something on a calendar.