If your water parameters are fine, nothing to worry about. Aro is not like other type of fish. They will take a long time to adapt to the new environment whether it's new tank or new water. Some Aro may go for months without eating. When I first got my Asian Aro, he didn't eat anything for a week. I tried some pellets at first. He grabbed those and spit them right out. I tried crickets the next day and he took those and asked for more. Your Aro is still young so he will start eating again soon. I personally wouldn't give my Aro cooked shrimp/prawn. Try to stay close to the food source that is readily available in the nature.
I've been feeding my Aro a variety of food. Crickets, MW, MW pupa, live shrimp/frozen shrimp. He will not touch pellets so I don't bother. Just give your Aro some time.