Can dogs become aggressive as they get older?

roosters fan

New member
I have a maltese x shitzu who just turned 8. As a young age, it has always been generally aggressive with other dogs and strangers in the house. Last month, the first time she has ever bitten anyone, my dog bit my sisters boyfriend and only yesterday she bit my brothers friend. Any reasons why this is happening? thanks
I forgot to add we have had a lot more people over in the last two months than usual, which she hates.
 
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