In recent decades, biblical scholars have shown convincingly that a key feature of the narrative depiction of Samson is the hero’s liminality, his status as a character caught “betwixt and between” two different worlds or states of being. Most often the discussion of Samson’s liminality draws attention to his perpetual location at the border between nature and culture or the worlds of men and women—freely crossing these borders, but never staying long on one side or the other. This article shows that a central aspect of Samson’s liminality has yet to be illuminated: the failure of this man-child ever definitively to cross the threshold into adulthood. The character’s impressive strength, rhetorical eloquence, and long hair are telling marks of manhood in ancient Israelite literature, as recent work on masculinity in the Hebrew Bible has recognized. However, alongside these manly traits Samson simultaneously demonstrates characteristics associated with boyish immaturity that point to a failure to transition to manhood. The article identifies the indicators of Samson’s immaturity through a close reading of the Samson cycle informed by the depiction of boyhood in the Hebrew Bible and by social-scientific research on male maturation. It then offers suggestions inspired by folklore studies on the possible purpose of tales of arrested development such as this one and its potential Sitz im Leben in an ancient Israelite context at the time of its original composition. The study concludes with a discussion of the literary function of Samson’s failure to come of age in Judges and the larger Deuteronomistic history.