Never. You don't need to introduce your child to video games. He will find them all too soon! video games can be addictive. Children who play them often withdraw from friends and family, avoid physical activity, and shirk homework. Studies show children who play violent games have a greater tendency to have behavioral problems. If permitted to play, set strict daily time limits, and enforce them.
Lay off them. Video games are unavoidable to kids as they will get exposed to them from their friends. The best you can do is educate them about them; perhaps purchase some games that you feel have some educational underpinnings, etc. But there is no way to avoid them being exposed to them.
After 4. Many experts state children should never play any video games that have any violence. Some experts have proven that children who sometimes play nonviolent video games also do better with reading, math, music, science, sports. Some games can be used to actually learn thinking and memory skills, improve knowledge in academic areas, performance in sports and other physical activities.