Is it true aggression or just over boisterous puppy play? Any training for him in the near future? Older dogs tend not to like being ambushed by younger dogs that have no manners and the only way that they will get manners is by you teaching them. Good Luck.
Misty- Samoyed Mix, Tannor- Golden Retriever CGC
Robyn- GSD CGC, TC, Midnite-GSD CGC,TC, Brennan-Golden Retriever CGC, Batman-Husky/Greyhound , Apollo-GSD