When is puberty delayed?

A 17-year 3-month-old male presents with concern for short stature. Patient is short, appears well-nourished, has no dysmorphic features, is normotensive, and noted to be prepubertal. Past medical history: Patient has  been well and has not had any chronic illnesses nor has he been on any chronic medications. Parents report that he has always been among the shorter children at school. Birth history: Patient was born at full term by normal vaginal delivery. His birth weight was 2.5 kg and his birth length is not available. Developmental history: Parents report normal developmental milestones. No history of delayed dentition. Diet history: Patient consumes about 1800 kcal/day. Family history: Patient lives with his parents and younger brother. No reported medical or hormonal disorders in the immediate or extended family. Social history: Patient is studying in twelfth grade and reported good grades. Physical examination: Patient is noted to be 147 cm tall (–3.5 SD below mean) and 40 kg (–1.88 SD below mean). No evidence of goiter. Patient is noted to be tanner 1 for pubic hair with tanner 1 prepubertal testicles. Other systemic exam is within normal limits. Labs  • Normal CBC, electrolytes, S. calcium and phosphorus, renal function, liver function and urinalysis  • AM cortisol noted to be 4.6 mg/dL, stimulated cortisol level 15 mg/dL  • FSH 0.51 mIU/mL, LH 0.10 mIU/mL, Testosterone <2.5 ng/dL  • Prolactin 11.44 ng/mL  • TSH 0.019 mcIU/L (0.6–5.5), fT4 0.6 ng/dL (0.8–1.7)  • Testosterone primed GH stimulation testing with clonidine noting peak GH level below 3 ng/mL.

When is puberty delayed?