Age
Because we are told that Colonel Fitzwilliam is “about thirty”, this man is likely into his thirties. We have no information about other siblings he may have.
Family and Situation
Because we are told more than once that Colonel Fitzwilliam is a younger son, we know he must have an elder brother who is also the son of the Earl of -------. Because of the way noble titles work, it is likely that this eldest son borrows one of his father's lesser titles and is either a Viscount or a Baron (with the former being the higher rank).
