just yesterday I had the idea about kid being shanks little brother (I know an old one, but it is about the argumentation):
Maybe Kid and Shanks parents got killed by some robbery back then, because people believed the one piece or at least some treasures of the roger pirates would be with shanks family. Since shanks was still not in the town, he didn’t witnessed, but Kid merely survived, but saw his parents die, because of his older brother.
So Kid is blaming shanks for the death of their parents, he hates him for this. This is why he also wants to overcome him. If anyone wants to get close to Kids family again, he shall deal with the strongest.
this is also why Shanks sticks to Luffy. He wanted to give the future to his little brother, to Kid, including the strawhat. But Kid refused, shanks wasn’t able to build any connection to his brother anymore. The bond was broken, so Shanks was looking passively for a new little brother, Someone he can give the future. Then he met Luffy, which triggered the memory of eustass before the accident. Luffy was like Kid was before.
And again, Kid is just a broken version of Luffy, an alternative Luffy.