Mr. Joseph Arthur Luis was fond of puzzles right from his childhood. A few months ago, he was caught puzzling his son's father-in-law, Mr. D'Costa. Mr. D'Costa just wanted to know Mr. Luis's age, but what Mr. Luis said was, "My grand-daughter, my son and I together are 140 years old. My grand-daughter is about as many days old as my son is weeks, and my grand-daughter is as many months old as I am in years. Now, Mr. D'Costa, I think you can figure out my age by yourself." What was his age? Provide a detailed explanation along with your answer.