I do not think it's natural for chameleons(veileds and panthers anyway) to mature and mate by six months of age. There's so many side effects to it (increased chances of MBD, increased reproductive rate, shorter lives).
I've seen veileds mate at 4-5 months of age. Many of these females are having their second clutch by 7-8 months. The increased growth rate seems to afect their reproductive rate - they just keep developing eggs and die young. Grow them slowly, so they mature at 9-12 months, and feed them lightly, and lthey'll live 5+ years, laying 2 clutches per year on average.
Of course, this is not practical for some situations.