An understanding of the age structure of scientific teams is important in the era of global aging. Age-based characteristics of teams determine the complementarity of skills and resources, team power and diversity, and division of labor, which shapes team efficiencies and thus team performance. However, the literature on age structure in scientific teams, and its relation to team performance is scant. Based on 54 million research articles published between 1970 and 2019 in MAG, this study provides the first historical large-scale analysis of age structure in scientific teams and its association with team performance from two dimensions, i.e., seniority and age diversity, in the past half-century, in engineering, natural sciences, medicine and biology, and social sciences. We observe the increasingly aging and diverse scientific teams over years across fields and team sizes of different levels. For most categories, mean age and age Gini have an inverted-U-shaped relationship with papers' citations in a ten-year time window. Furthermore, in most disciplines, after controlling mean age and age pattern, a flat or homogeneous age structure that is characterized by a low age Gini is related to higher team impacts. The findings of this study provide implications for the practice of team formation and team management in science.