यत्र काले त्वनावृत्तिमावृत्तिं चैव योगिनः।प्रयाता यान्ति तं कालं वक्ष्यामि भरतर्षभ॥
yatra kāle tvanāvṛttim āvṛttiṃ caiva yoginaḥprayātā yānti taṃ kālaṃ vakṣyāmi bharatarṣabha
Word by word
The verse says
I will tell you, Arjuna, the times at which practitioners who depart do not return, and the times at which they do.
In plain words
What follows is old cosmology, and it is honest to say so.
Six months of the sun's northern course, the bright half of the month, fire and light and day — these were held to matter for the soul leaving.
Krishna sets it out, and then, four verses later, does something interesting with it.
Where you've felt this · in growing older
Your grandfather would not begin anything important on certain days of the month. He could not tell you why those days and not others — his own father had told him, and that was reason enough. In every other part of his life he was a careful, practical man who checked things for himself.
Going deeper
Inherited lore is being reported here, and the reporting is not the same as endorsement.
The passage that follows describes two routes out of this life, keyed to the calendar and the phase of the moon. It belongs to a specific cosmology that most readers today do not hold, and pretending otherwise helps nobody. Commentators have handled it in three ways: literally, as symbol for clarity and confusion, and as a tradition being acknowledged before it is quietly set aside.
The third reading is the one the chapter itself seems to support, because of how the passage ends.
For a reader this is permission to slow down rather than skip. You are allowed to find a passage strange, sit with it, and still take seriously the book it is sitting in. That is how most people read the scripture of their own tradition anyway.