]I wonder (pretending I don't know how it ends), 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 (again, pretending I don't know how it ends) 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.

Only from what we know so far, Colonel Brandon has had plenty of opportunities to marry someone, if that were his object. "Mrs. Jennings had been anxious to see Colonel Brandon well married, ever since her connection with Sir John first brought him to her knowledge;"

Considering that the oldest grandchild is six years old, this means the Middletons have been married at least seven years--so Mrs. Jennings has been trying to fix up the poor colonel since he was 28 or younger!

Also considering that he is rich and particularly gentlemanlike and although not handsome also not unpleasant looking, I can only imagine that with Mrs. Jennings working on Brandon's behalf, there could have been any number of young women who might have been interested in "setting their caps" at him, whatever Willoughby and Marianne might think.

I think it's clear already in the story that--for whatever reason--the colonel has not been interested in getting married.

Mrs. Dashwood, however much she might be an attractive person, would very likely be past child-bearing age in that time, so could not provide Brandon (or anyone) with a family, sons or heirs, and has nothing in the way of a financial inducement that might make a younger man interested in a slightly older widow. We know that Brandon does not need her money, but it is not unreasonable to assume that a 35 year old man would like to have his own family.

There would seem to be no point in a younger man in marrying a 40 year old woman, however charming and pleasant company she might be, unless there were a very strong attachment to her. And we already know that Brandon is in the throes of a very strong attraction to Marianne, not her mother.