Michael Bryce, aka Arapaimag's 11 year old granny was 33" last year - you can find a Youtube vid where the fish is being measured when transferred from 15,000 gal into 52,000 gal. He has more than one.
They are peaceful, unfussy. Some say they can exhibit migratory behavior in tanks too, swimming against the current for months, which may be disheartening to witness but I never seen it with any of my many doradids.