when does one stop being a tinok shinoshba and become a non-tinok shinoshba?

Shalom, Thank you for your question. The concept of a “tinok she’nishba” refers to a person who was raised without the benefit of a Torah environment. Because of that, the way Jewish laws relates to them is with more “mercy” – and does not expect of them that which we might expect of someone who grew up in a Torah environment. The exact application of this concept, and the measure of “lack of knowledge” is not clear at all. It may well depend on when you want to use it, as the levels of ignorance may differ for different subjects. So, unfortunately, I cannot give you a straight clear answer. Perhaps if you write about the exact application and situation you are dealing with, we could perhaps give a better answer. Blessings.