.. becomes self aware enough and likely to have the capacity to make sound decisions, understand consequences of many of their actions, and learn to accept them in our culture?
It really is at about about 18. Some much earlier. Some never.
But most? About 18 or so.
I could imagine some other cultures, where kids are not coddled so long, and where kids are needed at a young age to work the land, contribute, and be responsible, where the necessities of life require that they mature faster (and they do) ... it might be a little younger.
But here? No. It's about 18.