new catch dog expectations

I expect a young dog say 6 months to try catching and mouthing piglets. A 8 month dog should be doing the same with 30 to 50lbers. Over a year should be catching and holding not regripping every 5 seconds. I was always told not to let ur bulldog catch anything much more than 50# until after a year in order to prevent damage to their teeth. I may have been told wrong and may go about it wrong but this is what I was told to do.

An unstarted dog over a year old I figure should get the general idea within the first 5 tries doing better each time.