Relative age effects (RAEs) are independent of specific cutoff dates that can vary from country to country. However, the consequences of changing the selection cutoff dates within a national sport organization are unknown. Further, the transition from international youth to senior representation is yet to be explored in rugby union. Thus, the aims of this article were twofold: "Study 1" compared the birth quarter (BQ) distributions of the England Rugby Football Union (RFU) under-18 representatives based on September to August and January to December selection cutoff dates. "Study 2" explored the BQ distributions within the RFU international development pathway through analyzing the under-18, under-20, and senior representatives, as well as the BQ distributions of youth players who were subsequently capped at senior level. Chi-square analysis was used to compare BQ distributions in each sample against expected distributions. Results revealed a corresponding shift of a skewed birthdate distribution favoring chronologically older players that was mediated by specific cutoff dates (p < 0.05). Moreover, whilst RAEs were present within both youth cohorts (p < 0.05), it was not apparent at the senior level (p > 0.05). Furthermore, during the transition from international youth to senior representation, more chronologically older players were successfully capped.