The organ implantation process begins from early adolescence and finishes roughly during very early adulthood.
There are 19 of such organs to be implanted, each of them designed to aid the Marine in being an all-terrain unstoppable killing machine, each engineered from the Emperor himself from the template of his 20 Primarchs.
Undergoing grueling selection processes designed to weed out all but the strongest and smartest, pre-teen males are then screened for the upmost genetic compatibility with the various gene-seed organs they will have implanted into them to turn them from ordinary boys into the ranks of the superhuman soldiers of the Imperium. The Adeptus Astartes, also known commonly known as the Space Marines are a breed of genetically-enhanced transhuman warriors engineered by the Emperor of Mankind for his Great Crusade.
