This is a personal decision but here are my points:
What do you mean by "he has exceeded in agility." I don't know about all the agility clubs, but AKC won't allow dogs under 18 months to compete so I'm not sure how much success your baby could have by age one. Does he have a MACH, is he ranked in his breed for agility, how fast is he (YPS), is he on the world team???
He has a lot of champs in his pedigree. . . is he a champion? What traits of his are so good that they need to be passed on? Do you know his weaknesses? No dog is perfect, not even a Best in Show winner so do you know what his flaws are? Do you know how to breed out those flaws? In other words, do you know if they are dominant/recessive traits, if they are prominent in his pedigree, etc.
Your dad doesn't want his line to end. . . would it really end? Does he have no half-sibling, aunt, uncle? What is so great about this line that other lines don't have?
Age one is the absolute youngest that I would breed a dog, but I don't see why one would breed a dog so young unless they really knew what they were doing. I like to wait 'til they are mid adults and have really proven themselves in wins and health tests. There are a lot of Aussie's in rescue, so unless you really feel your dog would produce really great Aussies, I don't see the point in breeding him just to do it.