The largest dovii in captivity, I have ever seen, with a TAPE MEASURE placed beside it was 19" TL (picture shown on this forum in an older thread). If I remember correctly, the fish was wild caught at a very large size, sold to another aquarist for big bucks, but died shortly after being purchased, for some unknown reason.
Anyways, one has to make a distiction between a guesstimate and an actual, true to life, measurement. One is a pretend made up number; the other, the actual truth. For a variety of reasons, guesstimates are often "out to lunch". Generally, people will estimate the length of a fish based on how big the fish looks and usually, as a rule of thumb, small fish get severely underestmated and very large fish, severely over estimated. No doubt, a large deep bodied male dovii, is a humungus fish for an aquarium, but IMO, is fairly unlikely to reach 24".
Of course there are always pictures of trophy specimens got on rod and reel in huge lake Nicaragua, but these are neither typical nor average specimens. Like any fish caught on rod and reel, the vast majority of fish caught are no where near record size.
IMO, realistically, 20" or less is about all one should ever really expect. Still a humungus fish when they get deep bodied. I'd love to see pictures of larger specimens in captivity, with A TAPE MEASURE placed beside it, but so far nobody has been able to show it!