The design and coding started in 2007.
Well it is speculated that Satoshi had posted on an internet forum about the concept of bitcoin in the early 2000's, around the time that paypal first came out.
As Cryddit says, we don't know for sure. Of all the possibilities though, I strongly favour the idea that Satoshi was simply telling the truth.
I personally don't think it was him in that forum post. I think it is more likely that it was just someone throwing ideas around after PP was becoming a 'hit'