What is the best age to introduce your kids to pet? I want to teach him reponsibillity by having one.

I think the best age would be when your child is able to take care of himself coz that's really important as only then would he be able to take responsibility of a pet. Responsibility can be instilled in kids in a number of ways such as asking them to take care of their books and personal items. You can also ask the to help you around the house. Gradually when you see that your child is becoming a little responsible, you can get him a pet too :)