Some mixes never become dog aggressive. Some are DA only toward strange dogs, some only males, some only females. There's no definite amount of aggression to expect in any dog except to just be aware that no matter what amount of time has passed where the dog has been dog friendly, any dog can "turn on" at any time. For example, my 8 y/o was almost 5 years old when he started showing signs of dog aggression. It's not all black and white.