For all the people saying clues don't add up, here are some facts.

1. McAllister is not middle-aged: according to the Collins Dictionary middle-age means this is "[...] usually considered to occur approximately between the ages of 41 and 60" and since Xander Berkeley is 55 years old, this argument is invalid

2. It doesn't fit Rosalind description (first part): Rosalind stated that RJ was "just under six feet" (which I doubt she measured with a measuring tape), and since Xander is 6 feet tall and considering that it was an approximation this is an invalid argument

3. It doesn't fit Rosalind description (second part): Rosalind stated that he has straight hair (which McAllister has), but some of you are protesting because he is semi-bald, although those are two independent statements I will play along; So, he is semi-bald, but was him when Rosalind met him?, I mean at the beginning of the show (5 years ago) he wasn't.