Our work aims to address the problems of designing health assistant applications that run on mobile devices. We discuss the lessons learnt through the design of a mobile application for use by 45-55 year olds, who will be the likely users of such assistive technologies within the next decade. Categories and Subject Descriptors H.5.2 [User Interfaces]: Prototyping, Screen Design, Usercentred Design General Terms Design, Human Factors Keywords Mobile Application Design, Mobile Healthcare