Hey there,
I just encountered the talon company, which tried to kill me, at the super mart near Springvale right after leaving Vault 101 @ levell 1. Apparently those guys spawn if you were able to disarm the bomb in Megaton (which I did not) or acquired good karma (which I apparently did [although I am not sure which quest in Vault 101 gives you 250 karma points]).
This encounter would make sense if you spent some time in DC and got some reputation, but is really questionable the other way around (you leave vault 101, someone immediately wants you dead).
So, is there a way to somehow postpone this encounter until you hit for example level 5?