I've only briefly kept juvenile Dovii.
They reach sexual maturity in about a year. I don't know how long it would take a male Dovii to reach maximum size. I'm guessing a few years.
Mine began eating fellow tankmates at three inches.
Sometimes fish can reach maturity much faster than you would expect. I had a pair form out of a batch of dovii growouts at 3 and 4 inches in size. I also bought 3 haitiensis at one inch, and then two of them formed a pair and spawned a batch of fry at 2.5 inches which I was not expecting.
There are a number of factors that influence growth and maturity.
One of the most important is your water change routine The less you make regular changes the longer it will take.
Many territorial species (like dovii) produce growth inhibiting hormones that can only be removed with water changes.