Like DForck42 already answered on how a Looper contract works, one who chooses the Looper profession also chooses to kill himself somewhere in future and to have a rich life from that moment on for only 30 more years.

On your question update, taking the Abe example: in the movie, it is never implied that Abe makes decisions on closing loops. But suppose he did, then the answer is very simple: he just has to remember to send that Looper back in time. It surely is his own decision; all he needs is a calendar.

Like DForck42 already answered on how a Looper contract works, one who chooses the Looper profession also chooses to kill himself somewhere in future and to have a rich life from that moment on for only 30 more years.

On your question update, taking the Abe example: in the movie, it is never implied that Abe makes decisions on closing loops. But suppose he did, then the answer is very simple: he just has to remember to send that Looper back in time. It surely is his own decision; all he needs is a calendar.