carded for life
Description of somebody, usually in their late adolescence, who looks significantly younger than their actual age, and in turn, upon suspicion of being underage, will be checked for ID for (jokingly) the rest of their lives.
Dave: You're telling me that kid is in grade 12? Or did you say that he is 12? It sure looks so.
Michael: Yea, he'll be carded for life.
Michael: Yea, he'll be carded for life.