At the beginning of the components that affect the performance of the swimmers’ training and race planning, the stroke count (SC), stoke lenght (SL) and stroke rates (SR) of the swimmers are important. For this reason, it is important for both athletes and coaches to know how to develop and change these characteristics with age. The aim of this study is to investigate the change in athletic performance and body structure of 9–15 age group. A total of 50 students were participated in the study. Subjects were divided into two groups as below 12 years of age (< 12 years, nmale = 14, nfemale = 14) and 12 years of age and older (≥ 12 years, nmale = 11, nfemale = 11). The athletic performance variables are grouped in such a way as jump (vertical and horizontal) and swim data (50 m free swimming time, number of SR, SC, SL). Descriptive statistics were used for the groups and Mann Whitney U test was used for comparison between groups (p < 0.05). A significant difference was found between all groups except SR, and in the jump performance (horizontal & vertical) with age. There was no significant difference in stroke rate and stroke time in kinematic parameters; as a result of the significant difference found in the SC and SL, 50 m freestyle swimming times decreased with age. As a result; it is thought that following this changing process for each age group of coaches will contribute significantly to the swimming performances of the athletes.