Much research is conducted for evaluating digital-based solutions for healthcare among older people. However, some older people are less likely to be involved than others. We present an analysis of participation in the evaluation of a mobile-based system for monitoring post-operative progress after a day surgery in Sweden. We explore key factors associated with the unwillingness to participate and discuss the possible role of self-ageism in determining the decision not to participate. Based on field information and survey data, we compared participants and non-participants in a sample of 368 individuals aged 60 and older and modelled the individual decision to participate (or not) in the evaluation. Decliners and those who were willing to participate differ along the lines of (chronological) age, gender, job, health status, and digital skills. Age remains a significant factor explaining individual decision to participate even when controlling for other variables. Overall results indicate that very specific groups of older people are more likely to participate than others in digital health research. Age plays a major role in the decision to participate or not. Negative self-perception of being old with respect to digital health research could contribute to explaining the individual unwillingness to participate.