Designing the age-65 boundary: who bears the cost when disability and aged care systems divide by age

Australia’s National Disability Insurance Scheme (NDIS) and aged care system are separated by an age-65 eligibility boundary that channels people with similar functional needs into different entitlement regimes, service markets, and assessment pathways. Policy responses have often treated this interface as a coordination problem between adjacent service systems. This article argues that coordination is only part of the issue: the age-65 rule also functions as a boundary-governance device in a layered welfare state. Engaging policy design scholarship on target populations, instruments, policy mixes and institutional constraints, the article develops a theoretical policy analysis and diagnostic heuristic for tracing how an eligibility boundary can translate formal classification into unequal support outcomes. Institutional layering creates nonequivalence between NDIS and aged care; boundary work translates that nonequivalence into administrative categories; street-level discretion handles residual ambiguity case by case; and policy feedback can stabilize the resulting arrangements. The analysis specifies three downstream design pathways: legal-entitlement discontinuity, supply-side market mismatch and discretionary coordination burden. The latter is the article’s main conceptual contribution: it names how the work of making the boundary livable is shifted to frontline actors, families and service users without matching authority, resources or accountability. The analysis explains why referral protocols and information sharing are insufficient on their own unless accompanied by attention to eligibility, bridging support, market alignment and boundary accountability. The Australian case clarifies a broader policy design challenge: how welfare states govern boundary populations when individualized support systems are layered onto older categorical care systems.