Good question. Kind of tough to tell. I don't think their mentalities change as they get older.
Sent from my iPhone using MonsterAquariaNetwork app
I try not to anthropomorphize the behaviors I see in my fish.
While they are unquestionably not like us, I think its fair to say that a fish's behaviors will change and develop as it gets older. A young monster fish's instinct will tell it that it is a candidate to be a prey item. A grown monster fish will have an aura of confidence to it that comes from being an apex predator.