Most amphibians and reptiles are fairly fast growers. WTF's are not an exception, but it all depends on the rate you consider "fast". From froglet to adult is about a year. Sometimes more, sometimes less. Typically, many factors can affect their growth, mainly proper nutrition and how often they are fed. Froglets grow fast for about the first year and slow down after that. If you are looking to breed though, it is recommended to wait until they are about three years old. Even though they may be about their adult svl (snout-vent length) at roughly a year, they still need to have the proper fat reserves and weight to breed, which can take quite a bit out of a healthy frog.