In September 1913 in Göttingen, Weyl married Friederike Bertha Helene Joseph (March 30, 1893 - September 5, 1948) who went by the name Helene (nickname "Hella"). Helene was a daughter of Dr. Bruno Joseph (December 13, 1861 - June 10, 1934), a physician who held the position of Sanitätsrat in Ribnitz-Damgarten, Germany. Helene was a philosopher (she was a disciple of phenomenologist Edmund Husserl) and also a translator of Spanish literature into German and English (especially the works of Spanish philosopher José Ortega y Gasset).  It was through Helenes close connection with Husserl that Hermann became familiar with (and greatly influenced by) Husserls thought. Hermann and Helene had two sons, Fritz Joachim Weyl (February 19, 1915 - July 20, 1977) and Michael Weyl (September 15, 1917 - March 19, 2011), both of whom were born in Zürich, Switzerland. Helene died in Princeton, New Jersey on September 5, 1948. A memorial service in her honor was held in Princeton on September 9, 1948. Speakers at her memorial service included her son Fritz Joachim Weyl and mathematicians Oswald Veblen and Richard Courant. In 1950 Hermann married sculptress Ellen Bär (née Lohnstein) (April 17, 1902 - July 14, 1988), who was the widow of professor Richard Josef Bär (September 11, 1892 - December 15, 1940) of Zürich.

Based on the above article, answer a question. How many years old was Michael Weyl when his mother died?
30