I don't believe the size of a ferret has anything to do with other health or genetic problems. The average age of my crew including the larger hobs and jills is around 8 to 10 years. The oldest being 13. Of course all ferrets eventually get old age issues but I haven't seen anything abnormal in the larger ones. Breed ferrets with genetics prone for certain diseases and that is what you will get regardless of the size. A reputable breeder is going to trace lineage and disease issues and will stop a line that shows illness history. [Posted in FML 6885]