Saw a lady coming down the lane with a Labrador on its lead. Thought I'd better put my Boy on his lead in case the lab was a problem or in training etc.
The two dogs met and had a sniff. Then my Boy went for the lab.
I'd have been so ready to assume that my Boy would be fine. He's a lovely soft old thing who loves everyone. I don't know why he went for the lab, unless he was a young entire male and he didn't like it. The lab was fine, carried on bouncing about. We meet loads of dogs and he's always fine, has a mooch about with them, no problem. Spent a couple of years doing the KC obedience program with no issues.
The lady was lovely about it, bless her. Said he was only defending me. I said no he's being a bolshy old git but that's kind of you.
My dog's not neutered and a couple of neutered males have gone for him - much to their owners major shock and surprise. The smell can be taken as a threat by a neutered male, even though my dog is a big baby who runs a mile if someone roughs him up!
So it may have been that. Or possibly your dogs just getting a bit grumpy in his old age.