Once a duckling hatches from its egg, it will take anywhere between 7 and 16 weeks for it to reach full size. This process depends on the specific breed of duck, with some growing faster than others. For example, a Pekin duck will mature quicker than a Muscovy duck.
Generally speaking, ducks grow fairly quickly compared to other animals. After just a few weeks, they will start to develop their adult feathers and will be able to fly short distances. By around 12 weeks old, they should be close to their full adult size and weight. However, they won't reach sexual maturity until they are around 6 months old.