In my book on Biblical chronology, Important Dates in the Lives of Jesus and Mary, I conclude that Mary died, rose, and was assumed 15 years, 2 months, and some number of days after Jesus’ ascension.
This is based largely on the writings of Blessed A.C. Emmerich.
Her age from conception to death was 63 years, 8 months, and some days.
the figure 72 i think comes from Ven. Mary of Agreda, whose writings I have not found to be chronologically accurate.