I have seen very laid-back specimens that were big and old - I think it depends on each fish, but they definitely are the boss in any tank, and some of them are outright psycho.
Mine "turned" overnight, at about 8 inches, and killed and ate all of her tankmates, including tarpons and chocolate cichlids (temporalis.) That was overnight.
After that, she's been alone - and has her own 300 gallon tank.
Thanks - I think she's cute too!