One of my side characters is an attending general surgeon. She's only barely older than her interns and she has to be extra tough because of that to be taken seriously. She's young because she was a child prodigy and actually skipped three or so grades when she was younger. I envision her to be late twenties to early thirties.
I want to have her young but I also don't want her to be so young as to have ridiculous for her to have the position she is in.
Search Terms I've used: "Average age attending physician," "average age attending surgeon." "youngest to be surgeon," and so on with synonymous words.