Performance differences between female youth handball players selected for national teams and non-selected peers are often linked to strength, speed, and power. This study aimed to compare the conditioning capacities and body composition of national and non-national youth handball players. The sample included 36 female players (17.13 ± 1.75 years), 18 national and 18 position-matched non-national players. Anthropometry, sprint and change in direction ability, vertical jump, upper- and lower-body strength, aerobic capacity, and body composition were assessed using standard tests and bioimpedance analysis. For normally distributed variables, an independent-samples t-test was applied, while for variables that did not meet the normality assumptions, the Mann–Whitney U test was used. Cohen’s d was used to assess effect size. National team players showed significantly greater jump height (p < 0.001, d = 1.408), higher relative peak power (p < 0.001, d = 1.644), and faster 20 m sprint times (p = 0.004, d = −1.037). No significant differences were found in body composition or the other measured parameters, although a moderate Yo-Yo IRL1 effect size suggests a potential practical advantage in aerobic capacity for national team players. These results indicate that explosive power and linear speed are key discriminators for youth national-team selection.