It varies - i.e. it depends on aspect (climate, light levels etc) but if planted out in the open usually within 15-20 years (obviously depending on the size of the initial plantings). In my garden I have P. ferox (an allied species) that were 1 m tall when planted in 1995 and they are now going adult at 4 m height 19 years later) - planted in the full sun, in free draining soil.