I highly recommend either taking a substitute postion and working your way through all the various grade levels you are considering, or just requesting permission to observe a few classes in the various levels to see what a typical day is like.
I teach high school and feel that this is by far the best placement for me. The subject that I teach at any level lower than high school would bore me to tears. If I do ever decide to change levels, it will be post secondary.
The decision comes from within. The best way to be informed it to get your feet wet.