I admire your scepticism, so please guesstimate the odds of being:
1. a renowned cryptographer capable of developing BTC. According to another renowned cryptographer, S. Haber, there are only 300.
AND
2. being familiar with Bitcoin in its early stages
These are 100% confirmed facts. We can even ignore his age and nationality. Still, I don't think there are more than a handful of persons who fulfill these two criteria. Please tell me where I'm wrong if you disagree.
1. Whether or not there are 300... Doesn't mean all 300 are publicly known or even have a Facebook profile. Satoshi does not have to be renowned. His use of anonymity shows at least that he cares little for being well known.
I personally believe any highly mathematically inclined person could give themselves the necessary education within years. So I would put the pool as: Anyone with large mathematical and computer science talent. Which is many, many, more than 300. (The secret sauce here is: the mathematical/compsci talent has to be combined with the *drive* and desire to create this system, but this doesn't have to come from a crypto/cypherpunk background. Maybe he was just some highly talented math guy who came to hate banks and then did some research and fell down the rabbit hole...)
2. How early stages? I would be surprised of a "renowned cryptographer" that didn't hear about it soon. It's their business presumably to keep up to date. So I don't see this concluding much.
btw, anyone know how old Nick Szabo is?