A 'beige lifer' is someone who lives a deliberately quiet, unflashy life — no exciting hobbies, no risk-taking, no drama, just a steady routine of work, walks, cosy meals and early nights. The phrase can be self-deprecating ('I'm a beige lifer') or mildly mocking. If your teen describes themselves this way, they are framing their quiet preferences in current slang. Harmless and arguably healthy.