My family hunts. The majority of meat eaten in our home comes from either hunting or fishing. As a result, their have been guns in our home since before our children were born, and they were in my parents home from the time they set up housekeeping.
Gun safety wasn't anything special when we were growing up. It was the way we lived. We knew where the gun cabinet was, where the key to unlock it was kept, and that the guns were not toys. We'd been to the gun range and shooting competitions by the time we were out of diapers. We were in the field helping flush birds before we started school. It was a way of life.
We have raised our children the same way. The only difference between my husband and myself and our children, is that everything we learned, we learned at the knees of our parents. We weren't required to attend classes, take tests, or carry certification cards. By the age of ten, our children both had attended gun safety and hunter safety classes and have the cards to prove it.
There is nothing wrong with beginning gun safety at a very early age. It is beneficial in the long run. If there are guns in the home or shooting sports are a common practice in the family, the earlier, the better.