Being at least 28 years old. Not kidding, well, maybe. In general, "seniority" in many fields in life comes with age; there is no shortcut. It's not very different in IT. Besides the accumulation of experience, with age you gain perspective and become more respectful towards your peers. You'll find many adults who have only one perspective (their own) and that are not respectful to their colleagues: these are not seniors not matter how much they know or how good they are.

Obviously, one also needs to have a bunch of good domain knowledge; but this is independent of age, and it's rather easy to acquire (just work harder/more).