["International Migration Review, EarlyView. ", "\nWe document the relative permeability of ethno‐racial boundaries between natives and immigrants who arrived at different stages of their lifecycle. The odds of crossing boundaries involving White spouses are highest among child migrants and lowest among adolescent migrants. By contrast, immigrants who arrive at older ages have lower odds of crossing the Black–Hispanic boundary in marriage. These findings illustrate the importance of the lifecycle timing of migration for marital sorting behavior and immigrant integration.\n"]