First of all, good for you and for him that he has seen so much growth all around!
With regard to mood disorders--it's not impossible to have a mood disorder at this age, although I would also approach mood stabilizers and any psychotropics with caution, especially where there are multiple diagnoses. I will say though, that CBT is absolutely a reasonable treatment option for young children, whether or not they are clinically depressed or anxious. For example, this highly-regarded teaching hospital has a whole clinic for CBT in children:
http://www.massgeneral.org/psychiatry/services/treatmentprograms.aspx?id=1982I have not personally used these tools, but know others who have had good experiences with them. If you can't find a professional willing to work with your child (which would, of course, be optimal), another possibility is to take some sessions of CBT yourself, and/or try using these workbooks with your child:
https://www.amazon.com/CBT-Toolbox-Children-Adolescents-Worksheets/dp/1683730755/https://www.amazon.com/Think-Good-Cognitive-Behaviour-Workbook/dp/0470842903/
