The global population is ageing and simultaneously the life expectancy at older ages is improving. To support healthy and active aging, it is imperative to find solutions to support physical activity (PA) in older age. Digital wellness technologies are a potential solution, but in order for such technologies to be successful, research is needed to gain a better understanding on their use and effectiveness among aged people. To address this need, this study investigated the effectiveness of a physical activity application to promote PA behavior among aged people of different demographics (gender, age, education, marital status). PA levels were measured before taking the application into use and after 12 months of use. The results suggest that a physical activity application can be effective in promoting PA behavior among aged people as there was a notable and a statistically significant increase in walking and total PA levels between baseline and 12-month follow-up. Regarding the demographic differences, there were very few differences in the changes in PA levels between different demographics, suggesting the effectiveness is not subject to the demographic background of the user.