Tom Riddle opened the Chamber of Secrets 50 years beforeHarry Potter and the Chamber of Secrets, which takes place in 1992. Because Riddle was in his fifth year when he opened the Chamber in 1942, he would have been 15 years old upon doing so. Fifteen years prior to 1942 is 1927, but as we know he was born on New Year’s Eve, his birthday would have to have been on December 31st of the previous year, 1926. Therefore since Harry Potter and the Deathly Hallows begins in the summer of 1997, Voldemort would have been 70 years old at the time! His death takes place at the end of that 7th book on May 2nd, 1998, meaning Voldemort died at the age of 71!