I have two Black Tri males. One is almost nine and has had seizures since 4 months of age. Still, he has three Rally titles and a couple legs of agility (I stopped running him in trials from fear he'd have a seizure on top of the A frame someday). My other one is six and a half and has two rally titles and is currently learning to track. My older one will pull a cart. both dogs have some herding experience. They both hike; the older one did a 130 mile backpacking trip with us when he was four, and they have both climbed several of the Adirondack High Peaks and numerous other mountains.
I absolutely agree that Aussies who are not properly socialized and trained and occupied are no fun to live with, and may be impossible. they are a special needs breed and not for everyone. Bloodlines have a lot to do with temperament, but socialization and training have just as much impact. A good Aussie is a fabulous dog!! Just be sure you are ready, willing, and able to give them the time and attention they need.