I think Minecraft shouldn't have an age limit, but we should be careful with a few things.
Little children shouldn't be allowed to play a lot on public servers, for example. It is both annoying for the players and the child. Most of the really little children I've met in Minecraft are swearing, trolling and spamming the chat. So they should be checked or limited.
But they could play in Singleplayer mode, or with their friends on a private server. It would be even useful; I think Minecraft is a really creative game, where You do everything, so children could learn creativity and determination.
To sum it up, I think children should play Minecraft with limits and under control.
I hope I could help.
