During the peak height velocity, it is crucial to adjust training intensity to optimize performance and minimize injury risk. This cross-sectional study compared external and internal intensities according to the type of training task (i.e., analytical tasks, small-sided games, and training matches). Similarly, the effect of these training tasks on the maturation age of young players was analyzed. Fifty-five U-15 and U-16 boys, representatives of two soccer clubs in southwestern Spain, were monitored using inertial measurement units and heart rate monitors. These devices reported data on training intensities. Their anthropometric data were also taken, along with the date of birth and measurement, to estimate the maturation age. To identify specific differences between groups, the nonparametric Friedman test and pairwise comparisons were performed using the Durbin-Conover post-hoc test. In addition, Spearman's rank correlation coefficients were calculated to better understand the impact of the variables. There were significant differences in favor of training matches in distance covered, maximum and average speed, and maximum and average heart rate compared to small-sided games and analytical tasks. In addition, high intensity actions and sprints were significantly higher during training matches compared to analytical tasks, and during small-sided games compared to analytical tasks. Player Load per minute was significantly higher during training matches compared to small-sided games, and during small-sided games compared to analytical tasks. Maximum speed, and maximum and average heart rate were also significantly higher during small-sided games compared to analytical tasks. Positive correlations between maturational age and high-intensity actions, accelerations, and decelerations were found, indicating higher intensity activities in more mature players. A negative correlation between Player Load per minute and maturational age suggests more efficient load management in mature players. No significant differences were found in distance per minute, sprints, speed, and heart rate, implying other factors influence these variables. These findings underscore the importance of considering biological maturation and the variability of training tasks in the planning and evaluation of the development and performance of youth athletes.