Can an adult sibling seek contact with a much younger sibling after the parents separate?

Yes. An adult sibling can apply to the family court for contact with a younger sibling using the same non-parent framework available to grandparents and other relatives - showing a genuine relationship with the child and that continuing contact serves the child's best interests. This can come up where, for example, an older sibling moved out or became independent before the parents separated, and the separation has since made it harder to maintain the relationship with the younger sibling.

As with other non-parent applications, the strength of the case depends on the actual relationship: how much time the adult sibling spent with the younger child, whether they played any caregiving role, and how the child experienced that connection. A significant age gap doesn't work against the application by itself; siblings with large gaps in age can still have meaningful, close relationships, and the court's focus stays on the child's actual experience of the relationship rather than the age difference. If a parent is limiting contact and you believe the relationship is genuinely valuable to the younger sibling, document your history together and speak with a family lawyer about whether an application is realistic.