All you've pointed out is that there are indeed fundamental differences of some kinds, but not of the sort kaens was talking about. The inconclusiveness you raise supports his point.
Edit: Wow. Downvoted. What on earth for?
There are, obviously, some population differences between men and women; for instance, on average men are taller. Blame the hormones. But people confuse mean and variance, and this is one case where instinctive ignorance of probability is tantamount to sexism. In fact, it's plain rude to do that to people.
Okay, an example. Let's say that on average, men are better fighters than women - whether that's societal or innate is neither here nor there, but take it as generally true. It doesn't change the fact that my sister could kick my arse. If I trusted in statistics there, I'd have been wearing my teeth as a necklace by the age of ten.
So even if the means are different, the variances are so high that you can't know what the person in front of you, male or female, is good at. What that means is that if you go into something like this with preconceptions based on gender, then you are being unfair to the person in front of you - male or female - by not judging them on who they are and what they can do. And if you fail to allow for the gender roles that society forces people into, then you're closing yourself off to talent. And if you close yourself off to talent you can use, your company deserves to fail.
I don't want to be that guy or that company.
(This is pretty personal for me, actually; my mother taught me BASIC when I was seven or so. She's a much better programmer than I am.)
However, what the OP and this thread are discussing is ways of 'fixing' a low percentage of women in startups. Which could be caused by either women on average having a worse skill set for startups or on average having less of a desire to take risky economic decisions.
If these are the causes then there isn't likely to be any way to 'fix' it.
Just because the claim is made that there are biological differences between men and women does not mean that the disparity of women vs. men in startups is entirely (or even mostly) due to biological causes.
If you want more women in startups then you have to either change women or change startups.
I think you should assume fundamental differences, because that's what both the research and experience show. Certainly more can be done for younger women, but if you don't think that businesswomen in their 40s are on average more capable than their younger counterparts then you probably haven't spent much time around businesswomen. (For reference, I took a class on women and entrepreneurship so I've been exposed to a lot of 20ish female entrepreneurs and a lot of 40ish businesswomen.)
As for which ones would prevent a woman from being successful as an entrepreneur in her 20s, it's impossible to say because success as an entrepreneur is multiplicative. There are dozens of factors, and only one has to be zero or near zero to make the whole thing fall apart. But the very fact that women are so different from men makes this theory quite plausible, albeit completely speculative.