It is a rule of thumb of one pound, one/half kg., for every month of age, so yes your kitten is very large for his age. I have had kittens that large, they remain large throughout life. They more than likely have the background of a large breed, like the Maine Coon or Norwegian Forest Cat. These cats can weigh close to twenty pounds when done growing. Or they may have a growth spurt now because of good food and upbringing, and quit growing between 9-12 months. Only time will tell with your big boy, keep us posted!
Given his features are fairly proportional, he might not grow much larger than he is now. Some cats will have early growth spurts, and finish growing as early as 8 months. Only time will tell at this point, though, it’s hard to say. Do you have any clue what size his parents were?
In general most cats are normally close to around 3/4 their full weight by 6 months. For example three of my youngest (they were strays so all I know is the mother was a black short haired and the father was likely a "large long haired orange tabby") were 4.4kg, 4.6kg, and 3.7kg at 6 months and are now about 7.7kg, 8kg, and 5.7kg at just over a year and a half (now that they are finally done growing).