Dmitri Mendeleev was 72 years old when he died in 1907.
Mendeleev died in Saint Petersburg on 2 February 1907, from influenza, at the age of 72. He had been born on 8 February 1834, so his death came only six days before his 73rd birthday. The dates can sometimes look confusing because sources may give the birth date in different calendar systems used in the Russian Empire, but the accepted age at death is 72.
By the time he died, Mendeleev had become famous primarily for developing the periodic system, first published in 1869. He arranged elements by recurring chemical properties and atomic weight, leaving gaps for elements not yet discovered. Later discoveries, including gallium, scandium, and germanium, helped validate several of his predictions.
His work extended well beyond the periodic table. He studied petroleum, industrial chemistry, meteorology, geology, and the standardization of weights and measures. In 1893 he became director of Russia’s Bureau of Weights and Measures, a position he held until his death. A common mistake is to remember only that he died in 1907 and estimate his age from the years alone; his February birthday had not yet arrived that year.