I obtained details of the marriage but not the actual record itself so no age was stated. They were married in St Johns, Laganbank. I have his approximate year of birth as 1862 which ties up with his age in the census but would only make him 16 when he was married (I wonder if his missus was in the family way!!)
The Devlins in the street directory you kindly provided are all mine. The only confusion is over Mary Devlin in the 1910 and 1918. Hugh's mother was Mary Devlin but he also had a daughter of the same name who appeared to take over 57 Little Patrick Street on the 1911 census. However, in the street directory she is listed as Mrs. but still using her maiden name of Devlin. I wonder is this is just an error. Hugh's mother would have been in her 80s in 1910 so I doubt it is her.
I don't know if the death index record for Hugh is the right one, but as he is missing from 1907 onwards I can assume it is. I will do more digging on this to see what I can find.