I think it's some of both. Certain breeds seem to be more flighty no matter how they're raised while other breeds just seem to be calmer. But, I'm a firm believer that if you want the best chance of calm, friendly birds you have to spend time with them....not just show up in their pen once a day to feed and water them.
Some breeds are flightier than others. For instance, I have cuckoo marans. As chicks, those are some of the most insane little freaks I have ever hatched! They run and scream every single time I put my hand in the brooder to feed, to clean, to cuddle, it doesn't matter. I exist only to eat them in a single bite.
However, my cuckoo maran hens, although they won't tolerate being picked up, they're not afraid. They will gather around me and if I have treats, they'll follow.
On the other hand, I have Black Copper Marans. These are my kitten breed. The chicks are sweet and docile. They don't mind being handled and they're very curious. As hens, they are very curious and also very sweet. They'll weave between my legs and even my roosters don't mind me squatting down to snorgle them.
Breed definately makes a difference. Some hens in the flippier breeds can prove you wrong though. It's a coin toss really. It depends on the breed and might even trickle down from the parent stock.
Well, I am hardly an Authority - having had my pullets for not even a year yet.
But Food seems to help a LOT.
My girls all pretty much ran screaming from me when I first got them @ 9wks old.
Gradually they have come around, which I attribute to treats.
They actually recognize the container I keep the raisins in - there's always a lot of discussion and interest when they see me carrying it.
And they know the bowl I bring every morning & evening has something more "special" than their pellets.
I can now pick each one up - ok, there is one holdout, but she's warming up too.
Now some of them even come to me asking to be petted or carried & 2 insist on being ferried from their roost to the floor of the coop every morning.
They also know where they live and it has become a lot easier herding them in that direction when they've been outside of the yard freeranging.
They will also come running in my direction rather than away - but again, that's probably because they are certain I'll have a treat handy
I've had chicks I handled daily ignore me later and I've had chicks I did nothing with except to fill their feeder become complete pests that wouldn't leave you alone for a minute. I say it's very heavily genetics/nature that determines the end result. Nothing I've done has had consistent results one way or the other. You get some slight differences between how easily a well handled or never handled chicken spooks at your movements and how fast they run away but overall they either have the personality to try coming up to you for food or to fight if they feel the need or they don't have the personality and no amount of bribing changes their flighty, spooky attitude. Also why I don't see how it matters whether you raise them from chicks or get adults. Within a few months they are either going to be as friendly as they would have or they would have grown up to act just as scared anyway. If you want friendly chickens look for breeds that people say are calm and friendly and you should get at least a few that enjoy attention. Otherwise buy some already tame hens.