That opting out [of creativity] that happens in childhood … moves in and becomes more ingrained by the time you get to adult life.

Kelley is describing creativity not as a rare talent but as a capacity many people gradually abandon. The “opting out” suggests a learned withdrawal—often prompted by criticism, grading, or social pressure—that begins in childhood when imaginative risk-taking is most vulnerable. Over time, that self-protective habit hardens into an adult identity (“I’m not creative”), narrowing problem-solving and willingness to experiment. The remark aligns with Kelley’s broader advocacy (as a design leader) for rebuilding creative confidence through practice, permission to fail, and environments that reward curiosity rather than correctness.