Yeh, mine is in a very similar place to Marilyn’s except on the right side and I never had it from birth either. Mine isn’t protuberant though…I think if they’re protuberant (stick out from the skin) and if they grow or change colour you should get them checked out.
Barbie, apparently Marilyn used to cover hers up in her earlier modelling career but eventually she started to darken it. Maybe I should do the same 
I have them all over my body as well…my arms and legs are covered with them, I have a few on my hands (one on the palm of my hand) and I even have one on the sole of my right foot! 