Some people are so changed by their life's experience that in old age they behave in completely unexpected ways. Many of us know elderly men and women who no longer act as we have come to expect them to act. I am not talking here about victims of senile dementia*. In the examples I am talking of the person continues to behave in what most people would agree is a normal manner, but one so remote from his old self that he appears, to those who know him, to be someone else entirely. (注)senile dementia:老年性痴呆
いかがでしょうか。 1文目 so 〜 that も「changed」の程度が具体的にどの程度かを右に示していますね。<具体化>
ここでは behave in completely unexpected ways
というところがこの段落のポイントで、以下の文でさらに具体的に展開されていることが分かりますね。
2文目のポイント no longer act as we have come to expect them to act