Depends how inbred the flowerhorn is, some that aren't too badly inbred can live 10-12 years, but the really fancy but severely inbred ones only live in the 4-6 year range. It sounds like your flowerhorn might be towards the end of its' life unfortunately
I don't know, I haven't gotten into flowerhorns all that much, all I know is the higher grade, more inbred ones live shorter lives than the lower grade, less inbred flowerhorns.I've noticed 'old' flowerhorns get that weird kind of pop eyed look with loose scales. Their nuchal hump sometimes looks like its shrinking and uneven. There's an overall loss of body tone too.
Not sure but I'd heard the more 'square body' strains live longer. Maybe around 8-10 or so.
Body shape has nothing to do with longevity.
Including the short bodies? I'd read much discussion about the overall effect of 'compressed' body types and compromised organs / digestive tract issues.