Adolescence marks a crucial period for the establishment of physical health and fitness, shaping future adult health trajectories. This study aimed to investigate the changes in health-related fitness concerning age among adolescent boys. A sample of 80 students aged 13-16 from Upashahar Maddhamic Viddalay, Jashore, was selected at random to assess health-related fitness components including low back and hamstring flexibility, abdominal muscle strength endurance, upper-body strength (chin-ups), and body composition. Fitness was assessed by measuring the components of Health-Related Physical Fitness as prescribed by AAHPERD (1984). In addition to these fitness components the body composition of the subjects was assessed by measuring triceps and subscapular skin folds, all their parameters were the criteria for measurement in the present study. Statistical analyses, including mean values, standard deviation, and 't' tests (where table value at .05 levels for of 38 was 2.02), were conducted to determine significant differences across age groups. The results indicate that abdominal muscle strength endurance, as measured by sit-ups, showed significant differences at .05 level between age groups, with class VII and IX exhibiting higher mean values compared to class VIII and X. This suggests that factors such as academic pressure and lifestyle choices may impact physical fitness levels among adolescent boys. However, when considering upper-body strength, flexibility, and body fat percentage, the study did not find significant differences between age groups. This indicates that these aspects of health-related fitness may be less influenced by age alone and more by individual factors or environmental influences.