Performance thresholds, efficiency, and access equity in junior girls' tennis: longitudinal analysis and bayesian forecasting of ITF rankings (2004-2029).

The ITF junior girls' ranking system shows accelerating cumulative thresholds (TRP) alongside less predictable efficiency-based patterns (PPE). Elite entry age remains consistently young, broader tiers are ageing, and access to P₉₀ is dominated by a small group of nations. Percentile thresholds therefore capture systemic competitiveness more than intrinsic ability, offering valuable but context-dependent insights for planning and equity in talent development.