This case study paper describes the development and evaluation of a prototype, Golden Jubilants, a smartphone app. Golden Jubilants was built within a software engineering in healthcare project, ReDEAP, that aimed to identify a set of recommendations for the design of smartphone apps for older adults aged over 50. Prototype development and evaluation is a recognized way to elicit meaningful feedback from any user group. This tangible artifact was interactive and provided fruitful engagement for us as researchers, and for the older adults who participated. This short paper presents the prototype evaluation process, and techniques used to ensure older adult involvement. To conclude, we discuss four key recommendations for consideration by software engineering in healthcare researchers who are using prototypes in their research - develop the research project through public and patient involvement, harness the potential of established evaluation and testing standards, develop a needed and tangible prototype, and involve an external group to evaluate findings.