rather than say what choices i'm limited to in a game that has "unlimited potential" i'd like to have to have the option...the people dont have to have the same roots, maybe your character was indeed born into the enclave, or maybe he is a raider. thats the thing...live with it, or not...i'd like to have the option there, even if i dont use it...roleplay dangit...roleplay...
I like the way Dragon Age (it's really the MMO style) handled it. Each race...could be factions in Fallout... has their own starting area, and in Dragon Age, each of those araes does a good job of presenting a background for the character. This background can make a difference during the game as well, in terms of dialogue choices, availability of quests, and even choices in equipment and such. Dragon Age doesn't go as far as it could, but it's a good start.
So, what sort of skills would a vault dweller naturally have? What about a typical wastelander, or a raider, or a BoS brat? How would an 18 year old from each of those backgrounds see the world and react to life situations? Game mechanics can nudge PCs in a reasonable RP direction without removing freedom of action for the player.
In Dragon Age, for example, the Human Noble background presents a powerful informal quest of revenge, and opens up some dialogue that reinforces it. The player need not select the special dialogue, but it is there. The city Elf and casteless Dwarf starts provide a a very different world view, and presents the RP opportunity to select dialogue choices to support that world view. A rogue character from a noble birth would certainly see the world differently than a casteless Dwarf would. Regardless, the player may continue to select any presented dialogue choices.
All of this requires development, of course, but I think it would be well spent here.