Although previous research has linked sibling relationship experiences to youth’s social competencies with peers, we know little about the role of siblings in youth’s romantic relationship experiences. Drawing on data from a longitudinal sample of 190 families, this study examined the links between sibling experiences and the development of perceived romantic competence from early adolescence into young adulthood (ages 12–20). The data were collected from 373 youth (50.7 % female) in home interviews on up to five annual occasions. Multi-level models tested the moderating role of sibling gender constellation in romantic competence development and the links between (changes in) sibling intimacy and conflict, and romantic competence. The results revealed that youth with same-sex siblings showed no change in their perceived romantic competence, but those with opposite-sex siblings exhibited increases in romantic competence over time. Controlling for parent–child intimacy, at times when youth reported more sibling intimacy, they also reported greater romantic competence, and youth with higher cross-time average sibling conflict were lower in romantic competence, on average. This study illustrates that sibling experiences remain important in social development into early adulthood and suggests directions for application and future research.