1. does the Navigo Decouverte includes also "direct 2" bus from CDG 2A terminal?
2. can I buy Navigo Decouverte in treminal 2A upon arrival?
3. does 15 yeas old boy pay like adult?
I'm not aware of the Direct 2 bus from CDG. If it's a private run company it is not covered by Navigo.
You cannot buy Navigo inside of Terminal 2A. Navigo is available for sale in the train station near CDG Terminal 2C & 2D. or from the train station that serves CDG Terminal 1 & 3 travelers.