Well if not whole Quran, at least any adults of any age can memorize the last chapter AMMA  in few months or a year. Its just an offer with motivation to have this blessed opportunity with some effort and take this parah in heart before leaving this world. I got full success in this in my Quran teaching carrier. The main objective is to have maximum Quran in heart before we left this world. How much knowledge we have of different skills, disciplines and technologies and all stored in us. So why not Quran? And I guarantee you that its also 100% POSSIBLE . The only things which is required is dedication and regular time for Last Chapter. At first we see how much Surah memorized by the student, then we make a sequence of Surah to memorize length wise. Easy ones in first phase then bit long and at the end longest surah in Amma Para. But there is not set pattern of this project; prefer to discuss with students and then decide mutually. We also try to do this effort with Translation. If they student became conversant with Translation and Arabic then we set this pattern otherwise the easiness of students kept into top consideration in all time.