The Japanese do this all the time, for some reason. You can never accurately guess the age of an anime or JRPG character by looking at them.
According to the wiki, Zin was 29 in Sky (year 1202). Kuro takes place 6 years later (year 1208), so he should be 35, but lol he now looks like he is in his mid 20s now, not his mid 30s. Then again, this is the same series that tried to claim that Cassius was 45 in FC.
Does this man look 45 years old to you? Or, to use an example from the upcoming game:
Does this man look 46 to you? Yeah he looks like he
might be in his mid 30s but no way he's 46.
Hardly anyone visibly ages up in this series. I think Tita and Renne are the only ones who do.