the writers might have wanted a "young" barnabas for the 1795 storyline
Even before the year Barnabas was born was revealed, I remember reading articles in which Frid commented about how much fun he thought it was playing Barnabas as a youth in 1795. At first I found the comments very odd - but then I thought back to the way Joshua treated Barnabas in Ep #368_369 (browbeating Barnabas over his worry for Josette because her arrival was two weeks overdue, belittling the concept of love, and declaring that a woman isn't a future) and the way Barnabas reacted to Joshua. It certainly wasn't the way a 40-something-year-old would react to his father - not even an overbearing father such as Joshua. And the fact that Jeremiah and Barnabas were supposedly the same age definitely made Jeremiah and Joshua's relationship make more sense. And with realizations such as that, I really began to question not only how old Barnabas was actually supposed to be when he was cursed but, indeed, how old, say, Julia was actually supposed to be because quite obviously the age of the actors seemed to have little to no bearing on how old their characters were supposed to be...