The short answer: it changes, but slowly. A meta-analysis of 127 studies that tracked attachment from infancy into early adulthood, retesting the same people anywhere from two weeks to 29 years later, found a correlation of about .39 between earlier and later measurements (Pinquart et al., 2013). That’s moderate stability: noticeable, but far from complete, and for many people the picture shifts over the years.
Attachment keeps moving in adulthood, too. In a study that followed the same people from adolescence into old age, attachment anxiety declined with age on average, most clearly in middle and later adulthood, while avoidance decreased gradually across the whole life span (Chopik et al., 2019). People who were in a relationship tended to be both less anxious and less avoidant.
So the more useful question is what actually moves a style. A style holds as long as experience keeps confirming it and shifts when experience starts telling a different story (Fraley & Roisman, 2019). The shift can go either way: serious losses can make someone more guarded, and good relationships can restore a sense of security.
