While there are always exceptions to the rule, children over the age of 10 I think would be better with them. I will admit that I had my first cavy at age 4, but I did not handle her and was assisting my mom with wildlife rehabilitation shortly thereafter. If around young children (elementary school), they should not be unsupervised and should probably be handled only by an adult. Again, it depends on the child and the role of the parent/adult.
I've heard different things about hormones in males, etc. But in my own fact-finding and experience -- I have not noticed a difference in male vs. female. It is more dependent on the individual pig. For instance, Hutch is more people-friendly, while Starsky must trust you before he'll warm up to you. I don't think it has anything to do with gender. I think the same is true for biting. They are rodents and biting is always possible. Particularly if the animal doesn't want to be held, etc.
On occassion, they have little "spats" over territory. Part of this would be alleviated with a bigger cage. They never truly "fight" and I think it's just part of living with your brother -- a little "sibling rivalry".
