Low drive dogs can "wake up" when they are older, but they are still low in drive and alot of work to get them to do bitework. The Rottie's I've seen seem to be more defensive biters, others just go into avoidance and act confused. Find someone that knows how to work with Rottie's.

Over Here in Belgium they use an old Sack, made of 'Hession'they flick in on the ground whilst the trainer is 'STANDING STILL'with the Pup on a Line or Leash 2m Long, the Pakwerker then flicks the Sack over the ground in front of the Stationary trainer The Pup is Chasing the Sack as it is the Pakwerker who is moving towards the Pup. Then they let the Pup have it or catch it
The Trainer then holds the Pup in a 'Come to Me'postition and he will let the sack go, then the Pakwerker will again taunt the Pup this time with the Sack rolled up and a hand each end of the Rolled up Sack he then comes in close, the trainer is still not moving off the spot the Pup is pulling towards the Pakwerker who comes in and the Pup Grabs the Rolled up Sack
The Palwerker pretends to pull on it if the Pup is very Young, a Pup the age of your Dog he would pull and play a little harder. then he lets it go and the Pup holds the Rolled up sack and the trainer runs him around in a circle ,
The Pup is again put in a come to me postition and the sack gently taken away.
one more time the Pakwerker does the same thing But after this the Trainer runs the Pup still with the Sack in the Pups mouth to the Car and the Pup lets go of the Sack when it gets there
This is what they are doing with Young Goran, But he is also mad about his Obly Ball
All the time these take is no more than five minutes, they do not allow the Pup to lose interest