After studying Economics at the University of Amsterdam, Aad Koster was employed as policy advisor at the former Dutch Care Federation and was associated, among other issues, with collective bargaining. Later he joined the National Association for Home Care and he was CEO of ActiZ, association of organizations in elderly care from 2008 until 2015.
From January 2016 Koster has several activities as an entrepeneur, advisor and member of Supervisory Boards of care-organizations. He is also president of the Dutch Association of Supervisors in Care, Cure and Social services.
He is now vice-president of the European Ageing Network (EAN). Koster represents EAN in the executive board of Social Services Europe (SSE).