The purpose of this study is to examine the difference between perception of affordances and motor performance in young adults (in their 20s) and aging adults (in their 60s, 70s and 80s). In the first experiment, to determine the distance which would be used in the second experiment, we examined how viewing distances affected the perception of affordances on a stepping-over task. As a result, we found that a 4 meter distance was suitable for the following experiment. In the second experiment, we compared, in young adults and aging adults, the perceived maximum height to the actual maximum height of a bar which the subjects could step over. We found that for the stepping-over task the perception of affordances did not show a generational difference, while the actual motor performance did. In particular, aging adults older than 80 years showed this difference more clearly. This suggests that if young adults can estimate their motor performance precisely, then motor perceptual ability progressively declines in aging.