I have two sons 18 and 16 and I think it is fairly normal to get a one word answer to a question! When I press for more the eldest tells me "It's all right, I've got everything under control" and I guess, well, I just have to accept that and trust that he knows what he is doing. Letting them take responsibility for their lives. He also is a quiet one and started working part-time this year and it has done a lot to develop his "life skills" that studying doesn't provide.