good question, I would also like to know the answer. i know some of them, like fischer were far above anybody their own age, even in the early teens, but I cant speak for the rest.
what were the greats like starting out

but fischer was also absessed with chess at the age of 6 so by his early teens yes he was ahead of everyone else was it because he had spent much more time studying than others even though they were older? im wondering what was kasparov or fischer like just after they learned how the pieces move before they got heavy into their studies
The earliest games are hardly preserved. This is Kasparov at 10, when he still was Weinstein and just had met Botvinnik. The game feels very mature and systematic, as if it was played by some old GM:
http://www.chessgames.com/perl/chessgame?gid=1069558
recently ive been going over a annotated game collection and while going over some of kasparov's games i cant help but be blown away by how good he is, i mean every move has multiple purposes and creates immediate threats that his oppenents have to deal with never giving them time to work on there own game until eventally it becomes to much and their crushed by the power of his attacks(and he's doing it against the best in the world). and i cant help but think what were the greats such as kasparov, fischer, tal and even the greats of today like kramnick and vishy like when they were just starting out? was it instantly apparent that they would rule the chess world or were they similar to the average beginner but maybe just picked up on stuff a little faster and devoted much more effort and time to the game than most until they got to world level?