This is a good restatement of the author’s conclusion. The evidence given supports the idea that less estrogen in old age leads to a higher Alzheimer’s risk, which the author presents as an alternative explanation to the life span theory.

The relationship between Alzheimer’s and age is not the central focus of the argument. The author’s point is to support a hypothesis that might explain this correlation, not to prove that the correlation exists to begin with.

This is not stated in the argument. It might be implied by the relationship suggested between Alzheimer’s and estrogen. Even then, there could be other factors we don’t know about.

This is stated as support for the author’s claim that estrogen levels may explain the difference in women’s and men’s risks of Alzheimer’s, and nothing else supports this claim. It’s a premise, not a conclusion.

This is never stated, and is generally a much stronger claim than anything the author says.