Satan was still kicking around the heavenly realm as far into the bible as the book of Job. Read all of Job chapter 1 and 2.
Then when was Satan finally given the heavenly heave ho?
Well read A book of Revelations, chapter 12, all of it.
That was written by John the Favorite Apostle for a revelation of a future time.
But, that future Time has since come about.
No Satan was not tossed at the very beginning, but God had good reason..
If He got rid of Satan in that Instant that Satan sinned. God would have appeared to be a bully.
No free will given after the promise of free will.
So God let sinful man and Satan rule themselves, until now.
When it is really obvious Man has ruled Man to his own injury.
Book of Ecclesiastes chapter 8 verse 9.
Simple, we have free will to choose Good, or to choose Bad.
We are not robots.
BUT, we will reap the rewards of our choices, have no doubt about that!