Dear Mr. Fecher,
Thank you for posting your request on History Hub!
The official World War II lists of WWII Army and Army Air Force Casualties and World War II Navy, Marine Corps, and Coast Guard Personnel Casualties do not provide the age or birth dates of casualties. We are unaware of any official sources that provide these statistics.
We searched online and located Congressional Research Service report American War and Military Operations Casualties: Lists and Statistics. This report provides the total number of casualties for World War II broken down by service as well as by state, however it does not break the numbers down by age. The report does have age information for more recent 21st century conflicts. We also located Army Battle Casualties and Nonbattle Deaths in World War II: Final Report, but this report does not include age information.
It may be possible to find this information by reviewing each of the individual casualty files of the various services. Given that there are hundreds of thousands of relevant files, this would be a substantial research project. Limitations of time and staff preclude our reviewing the large volume of records that pertain to your inquiry.
Army Individual Deceased Personnel Files (IDPF) from 1940-1976 for personnel with surnames that begin with A-L are in the custody of the National Archives at St. Louis (RL-SL). Navy and Marine Corps casualty records from 1940-1989 are also in the custody of RL-SL. For more information, please contact RL-SL via email at email@example.com.
Due to the COVID-19 pandemic and pursuant to guidance received from the Office of Management and Budget (OMB), NARA has adjusted its normal operations to balance the need of completing its mission-critical work while also adhering to the recommended social distancing for the safety of NARA staff. As a result of this re-prioritization of activities, you may experience a delay in receiving an initial acknowledgement as well as a substantive response to your reference request from RL-SL. We apologize for this inconvenience and appreciate your understanding and patience.
For Army IDPFs from 1940-1976 of personnel with surnames that begin with M-Z, please write to U.S. Army Human Resources Command, Casualty & Memorial Affairs Operations Division, ATTN: AHRC-PDC, 1600 Spearhead Division Avenue, Department 450, Fort Knox, KY 40122-5405.
We hope this is helpful