Individuals diagnosed with borderline personality disorder usually seek for treatment as adolescents or young adults. As age progresses, longitudinal studies suggest that borderline patients improve psychosocially, suggesting that they may somewhat belatedly achieve the milestones of young adulthood. Affect regulation may be particularly subject to major changes in young adulthood, as the prefrontal brain areas involved in affective processing underlie maturation processes up into the late third decade. From studies in healthy volunteers we know that that the capacity to process positive affects improves with age. Young adults with borderline personality disorder, however, display a negativity bias in emotion recognition and they have difficulties in inhibiting the recall of negative information. Neuroimaging data suggest that they suffer from deficient implicit affect regulation but they are able to profit from explicit strategies to suppress negative emotions, an observation which could have interesting implications for treatment. Regarding future research more efforts on developmental psychopathology on the one hand, brain maturation on the other will help to further understand the nature of borderline personality disorder. Regarding clinical issues early treatment designed to foster affect regulating competencies and self-esteem and to develop interpersonal skills might benefit young patients diagnosed with borderline personality disorder.