How old is Justice Stevens?

99 years (1920–2019)

Full answer is here. Hereof, when did Justice Stevens die?

July 16, 2019

Also, how did Justice Stevens die? Complications from a stroke

Then, how old are our Supreme Court justices?

United States Supreme Court Justices

Justice Date of Birth Appointed by
Samuel A. Alito, Jr. 4/1/1950 Age: 69 yr 10 mo George W. Bush
Sonia Sotomayor 6/25/1954 Age: 65 yr 8 mo Barack Obama
Elena Kagan 4/28/1960 Age: 59 yr 9 mo Barack Obama
Neil McGill Gorsuch 8/29/1967 Age: 52 yr 5 mo Donald John Trump

When did Justice Stevens retire from the Supreme Court?

Stevens retired on June 29, 2010 as the third-longest-serving justice in the history of the Supreme Court with 34 years and six months of service and just three days short of tying the tenure of the second-longest serving justice in history, Stephen Johnson Field (1863–1897) who retired in December 1, 1897.