Agree with others that it's a male (the head to body ratio supports that). Would appreciate a photo of head from the side. Do not pay much attention to what shop told you; they are wrong in all counts. Frog looks healthy; but if really 1 year old should be larger if a GABF. Do read the article Colleen/Jerrod linked; that will get you started right.

Remember to mix the substrate with dechlorinated tap only. Main thing is to feed a varied diet based on night crawlers and dubias/crickets. The latter should be gut loaded with lettuce, carrots, oats, and cherios for 24-48 hours before feeding. Insects should be sized same as distance between frogs eyes or smaller. IRT mammals, can give a small one once a month. Too large a mammal can rot inside the frog before it can be digested and kill it. Can use this guide for dusting food: http://www.frogforum.net/food-feeder...schedules.html. Good luck !