When does a baby bump usual pop up?

I was curious as to when a baby bump usually decides to pop up? My step mom is on her fourth baby and she's only about 12 weeks and she has the cutest little bump!!

I also have a friend whose about 12 and a half weeks along and hers is pretty prominent already (this is her first).

Whereas my mom didn't start getting one until like 14/15 weeks along.

What's the average? I know all women are different. I'm not pregnant, just curious!