I get my pups started on walks immediately after I get them at 8 weeks. Yes, there is a risk of parvo, but that risk is not nearly as great as the risks you run of behavioral issues if you don't get them out and socialized. That doesn't mean you have to put your pup in obvious danger. Just be smart about where you walk him. Keep him away from dogs you don't know, away from high traffic dog areas (dog parks, places where dogs potty frequently), and away from any animal fecal matter (dog or other) which is largely where most virus and illness is shed.