I.e. the career you are in now (if you are (yet)). For me, it was rather late in life-I originally wanted to be a biologist, but frankly I have very little patience for the minutae of the field, but noticed during 1-1 conferences with my students (as a TA) that they easily got concepts that eluded them during lectures and labs. Something “clicked” with me regarding that, and I’ve been a tutor ever since (age 38). Before even the biology track tho I was all over the map (I must have had over half-a-dozen majors by age 30), but nothing ever “stuck” with me like tutoring has.
I have some kids who know very early-and it’s obvious that they’re 100% sincere and serious about it. I have a 2nd grader right now who knows that she’ll be a paleontologist (yes she used that word to tell me) A few years ago another 2nd grader told me he wanted to be a “movie star”; when I pressed him for details, it turned out he meant “special effects guy”, but didn’t know how to say that (spent a lot of spare time between lessons drawing some very stylish alien creatures).