Not much was mentioned about Adam, but he appeared to be eight years old in the second book of The School for Good And Evil. He was elder than his younger brother Jacob for two years. In the Last Ever After of The School for Good And Evil, Jacob appeared to be not more than seven or eight years old. So Adam may be about nine or ten years old in the last book.
Like Jacob, Adam was loved tremendously by Stefan probably because they were his own children. He was despised by Sophie partly because of her hatred towards his mother, Honora.