] I wonder ... if CB and Mrs. D could form an attachment? I can't talk about his true personality yet, so maybe they really aren't suited for each other, but I wonder if there could eventually be anything between them? I can't imagine it was totally unheard of for a man to marry a woman who was only a few years older than himself.

There is one unanswerable reason why they cannot marry. The Dashwood family tree is already too complicated. The book already needs a family tree to illustrate Chapter 1; with Mrs Dashwood remarrying the chain of stepmothers and stepfathers would be too much for the average reader to comprehend.