I don't know if that tank would ever get 'too small' for a male dovii - they do grow very large, however. A 28" wide tank does help give you some leeway over a 24" tank, but if the male dovii in question is pushing 22+", then you may feel like a 30-36" width would be best. Honestly though, your tank would do very well for a good long time and you'd be able to have a long time to see whether or not the one you grew out would ever attain monster size. I have heard of some males topping out at 18", and some that are over 25". Depends on genetics and tank conditions.
Well I live in Australia and I will never get a wild caught or f1 dovii I've been told that fish breed in captivity don't grow as big as wild ?