That's an excellent question, actually. My headcanon tends to be that Albert always sort of knew he was headed for the FBI, if only because his ultimate goal was "I want to make the world a better place; how do I best apply the strengths and qualities I have to achieve that?" The ultimate goal of furthering the cause of good is something he derived from contact with his (entirely headcanoned) grandmother in his formative years, and it was in high school that he ultimately figured out his strengths were in fields of science. He's always been highly detail-oriented and it honestly probably didn't take him very long to put together the idea that skill in forensics means stopping more criminals means less evil on the streets means world is a better place. So yeah, I think he always kind of knew that the FBI was going to be the place for him; I can't imagine the private sector appealing to him as much, since his interests seem to be focused more strongly around the pursuit of justice than the pursuit of science for science's sake.

That said, if he wasn't in the FBI — and actually, this headcanon extends to even after he decides to leave the Bureau at some point, retirement or otherwise — he'd be a professor at some esteemed institution of higher learning. The thought of Professor Rosenfield really appeals to me and I just can't shake the mental image of Albert delivering snappy impatient raegfurious lectures to a packed lecture hall full of frantic students and demanding perfection from his lab assistants and generally raising up the next era of forensic pathologists on the rationale that if they've got to hand off the world to someone, it damn well better be to a generation that's equipped to handle it, and by "handle it" he naturally means "to his own high and lofty specifications".

I feel really bad for all of his students.

But Professor Rosenfield totally needs to be a thing.