Our solar system was formed by matter spinning in a nucleus cloud and as materials colided off one another, they formed planets, and as the cloud began to slow, orbits. At least, thats the really general version of it.
So literally, they formed realativly at the same time.
Who knows! I did a report on Jupiter back in 5th grade (That was a while ago damnit)
It's an awesome planet! You know it was almost a star, but it didn't have all the ingredients required so it became a huge meteor sucking ball instead.