It is well known that the Chinese writing system lacks visual cues for word boundaries, such as interword spaces. However, characters must be grouped into words or phrases for understanding, and the lack of interword spaces can cause certain ambiguity. In the current study, young and older Chinese adults’ eye movements were recorded during their reading of naturally unspaced sentences, where consecutive words or nonwords were printed using alternating colors. The eye movements of both the Chinese young and older adults were clearly influenced by this explicit word boundary information. Across a number of eye-movement measures, in addition to a general age-related slowdown, the results showed that both groups benefited overall from the explicit color-based word boundary and experienced interference from the nonword boundary. Moreover, the manipulations showed stronger effects among the older adults. We discuss implications for practical application.