He's a baby..don't feel bad. In the future just go with your gut if you think that he will react in a way you don't want. As they get older they stop with the mouthing.
Misty- Samoyed Mix, Tannor- Golden Retriever CGC
Robyn- GSD CGC, TC, Midnite-GSD CGC,TC, Brennan-Golden Retriever CGC, Batman-Husky/Greyhound , Apollo-GSD