Generally speaking Nurse Sharks tend to grow faster in captivity than they do in the wild - mostly because of the following reasons - More regular feedings & more contant water tempratures.
In the wild Nurse Sharks may take 12-20 years to reach maturity, In Captivity - it more like 5-8 years on average. In captivity young Nurse Sharks may average about 12 inches per year - til maturity.
As for tank sizes - at 12 inches long - the Nurse pup is either about out grow the 100 gallon tank or it will in a couple months. In theory the pup should be able to stay in the 400 gallon for at least a year - depending on the actual dimensions of the tank.
A 10ft diameter pond would likely be good for a couple of years.
Remember though - Nurse Sharks reach maturity at about 2.1-2,4 meters (7-7.8 ft) - and may eventually grow to be about 10 ft or more. So to keep one for life - basically requires a large swimming pool-size shark pond.