We examined the correlations between aerobic fitness (assessed by the 30-15 intermittent fitness test, IFT), maximum isometric strength, vertical jump and speed performance of thirty-seven under-16 (U16) Welsh regional rugby players. The physical assessments employed in this research are part of a Regional development program under the auspices of the players’ development pathway created by the Welsh Rugby Union. The tests were performed in the following order: vertical jumps, isometric mid-thigh pull, 40-m sprint velocity, and 30-15 IFT. A Pearson product moment correlation coefficient was used to estimate the magnitude of the relationships between the different physical variables. Overall, we found significant associations between jump height, sprint velocity, maximum isometric strength, and 30-15 IFT performance (r ranging from 0.44 to 0.70). Moreover, strong positive interrelationships were observed between strength, speed, and jump qualities (r ranging from 0.51 to 0.80). Although these findings remain to be established in prospective studies, it seems that U16 athletes are capable of simultaneously improving their aerobic fitness and neuromuscular performance. This can be confirmed by the close correlations between the 30-15 IFT and every neuromechanical parameter reported here. Therefore, practitioners are recommended to use multifaceted training schemes with their young rugby players, including different components of endurance, speed, strength, and power training.