All bearded dragons, regardless of age, need part of their diet to be live insects. Younger dragons need 80% live protein in their diet, while adults only need 20% live protein in their diet; your dragon will never stop needing to eat live bugs.
Yes, your bearded dragon can swim very well. Most love swimming and playing around in the water. Some may need time to get used to the water while some are afraid of it and never seem to be able to get over it.