Most Coastal's that are pure will max off at 7-8 ft, with those being on the larger end of what to expect. There plenty that will stop shy of 7' and produce offspring, and be healthy. Same to say even 6'.
My 2011 Pure Coastal Jag is just over 6' right now (female) and my 2011 Pure Caramel Coastal is somewhere between 4-5 ft. He was born around July, the female was born in March FWIW.
People may say that if you feed them hard they will grow quick, but mine have rarely missed a meal eating weekly, and bi-weekly some times for the female who is one of my garbage disposals for BP rejection corner. So they are fed pretty good compared to some feeding schedules. Carpets are just one of those species that do take 2-3 years to get to maturity. My 2012 IJ's that were born in June 2012, my male is still under 2' and eating weined rats. And my female is 3' eating small rats. . . . the female has never missed a meal, the male granite was quite picky as a hatchling, but pounds food weekly now.