I would say yes that is normal. Our 4 year old is a "grumpy old man" already. What you have to do is take dominance. They start to think they are untouchable. After an incident, Firmly but gently secure them to the ground. Usually by back of neck. They have to be on their back.. hold them there amd firmly say their name and then NO, bad dog. Hold them there until they submit. May take 30 seconds, amd they will fight you for it... they cant win. Dont be mean or abusive, but you do have to be alpha dog. I find I only have to do this about once a year, and our grumpy old man remembers. He respects me, and still loves me. It's hard to do, but needs to be done, as the alternative is alot worse.