This study examined age-group differences in eye movements among third-grade, fifth-grade, and adult Japanese readers. In Experiment 1, Japanese children, but not adults, showed a longer fixation time on logographic kanji words than on phonologically transparent hiragana words. Further, an age-group difference was found in the first fixation duration on hiragana words but not on kanji words, suggesting character-type-dependent reading development in Japanese children. Examination of the distributions of saccade landing positions revealed that, like adults, both third and fifth graders fixated more on kanji than on hiragana characters, which suggests that even young children utilize the same oculomotor control strategy (the kanji targeting strategy) as Japanese adults. In Experiment 2, we examined whether the proportion of kanji characters in a text affected adult reading performance. Japanese adults made more refixations and regressions in texts with a high proportion of hiragana characters. The results of both experiments suggest that differences between kanji and kana affect the reading efficiency of school-age children and that maturation of reading skills allows adults to optimize their strategy in reading kanji and kana mixed texts.