Yes it is, too ! What you said in your message was perfectly true. The further we look, the further back we are looking in time, and we cannot see further and older than around 380'000 years after the Big Bang because the Universe was opaque before that. So an object that formed and emitted its first light some millions of years after the Big Bang, but whose light has to travel more than 13.8 billion light years (the Universe is 13.8 billion years old), is not visible by any telescope.