Sorry for replying much later.
I think we can estimate Hugh/Hugo & Damian’s ages by what the past chapters stated.
We know Lucia & Hugh’s age when they married were 18 & 23, respectively, from the first chapters of the story, book 1 (I think it’s mentioned from chapter 1 or 2).
Not long after, Hugh brought Damian home (to Roam, in the North) & met Lucia for the first time (when Lucia was about 18-19 y.o, and Hugh 23/24), And it mentioned that Damian was 8 y.o at that time.
That means, the age difference for Hugh/Hugo & Damian was about 15 years.
It also mentioned that Lucia (and some other people who know the father-son relationship between Hugh & Damian) thought that Hugh was too young to have a son at Damian’s age.