Age of closure of spheno-occipital synchondrosis:

Postnatally, the posterior cranial base becomes longer primarily due to growth at the spheno-occipital synchondrosis. Histologic studies have shown that the spheno-occipital synchondrosis fuses at approximately 16 to 17 years in females and 18 to 19 years in males. Ref: Graber LW, Vanarsdall RL, Vig KW, Huang GJ. Orthodontics: current principles and techniques. Edition 6 page no 10