Having age ratings is useful so I dont have to play a game to know its age suitability. Its common for very young children to play games, and age ratings help parents make informed responsible decisions. There are some dark addictive patterns being used in gaming such as changing the odds of reward to optimise engagement (and make money) - these patterns need an age rating. Additionally, I think age ratings encourage developers to avoid content which would increase the age rating, since they then target a wider audience.