Can a six month old pitbull get parvo?

Yes there is no age limit. Up to date vaccines are the best prevention.  Did your puppy recieve their puppy sets on schedule (every 3 to 4 weeks from at least around 8 weeks until about 4 or 5 months)? If not your pup would be high risk as they don't have any protection and puppies aren't considered protected unless the vaccine schedule is followed. One or two early sets and they are still very high risk. If you think your pup may have parvo see your vet today. The sooner it is diagnosed the better their chances.
q9437991.html
http://www.apbtconformation.com/ http://www.apbt.info/tiki-index.php
http://www.wildheirlabradorrescue.org/readingroom/what-is-a-back-yard-breeder.php 
http://members.tripod.com/antique_fcr/goodbreeder.html
http://www.petfinder.com/index.html