The only reference I have is when someone like Piper or Macready acknowledges the fact that time has passed.
Whatever it is, it's definitely a prolonged period, because they make reference to things like "we've been together a while now" etc.
When I met Billy (the child Ghoul), my first thought was, I hope he's a Settler, I've got lots of advlts, but this might be my first kid Settler!
Unfortunately for me, his parents were also Ghouls and still alive, so he went to live with them.
A shame I couldn't invite all 3 of them to Sanctuary Hills.
It would be a lot safer then in a half derelict house with roaming Slaver gangs nearby.
Who are the Wilkins?
The only reference I could find that's currentish is Jas Wilkins (Fallout New Vegas).
And now I'm imagining Nat befriendling Billy, it would be interesting to see her having a Ghoul as a friend.