Strength and balance exercise is recommended to offset the physical and cognitive decline associated with an increased risk of falls in older adults. Active computer gaming (ACG) may be a potentially safe and enjoyable way for older people to participate in exercise. Involving older adults in the development of a bespoke ACG system may optimise its usability and acceptability. This paper describes the user-centred design of a system iteratively developed to deliver strength and balance exercise in older adults and suitable for display on a flat screen or using an Oculus Rift virtual reality headset. User testing of a prototype of the system in n=9 older adults indicated the safety, usability and acceptability of the system, with a strong preference for the screen display reported by users. Findings were used to modify the ACG system.