Responsibility vs Independence

[FishFishRevolution]

I was thinking about this the other day, when does a person have the right to choose for him/herself?
People should idealy make decisions bearing consequences that affect themselves. They should be able to make those decisions if they can accept the consequences, right? But what if the person is not old enough or mature enough to understand the effects of their decisions? Someone should guide them, right? Or limit their decision making powers...?
What if, they understand the consequences to themselves, but they don't factor in the consequences to other people, or the environment, or anything else? Should that power be once again limited? And by whom? Who has the unclouded clear judgement to make that call?
One last thing, what about decisions made by people, who's consequences harm themselves? This then affects people who love them, so is that not a consequence for others as well?

WHERE DO WE DRAW THE LINE?!