Best place to look is at the National Archives in Maryland. There are researchers that you can hire who live close by that you can get to go for you. Keep in mind when I was there in 1995 they were taking about 250 dollars and hour to do research. There is a list that you can get of the approved researches to find the information and are generally very good
Try familysearch.org. Below is his WW 1 registration info. Accounts are free but you need to register.
It says he was living in Tennessee in 1917 so there's that. If you know his wife's name that may help too. Sometimes if you look up the spouse you get more information.
Dear Mr. Overton,
Thank you for posting your request on History Hub!
The Georgia Department of Public Health Vital Records Office maintains birth and death records filed from 1919 to the present. Some counties may have older birth, death, marriage, or divorce records in their files, but county files only contain records of vital events that occurred in that county. Therefore, we suggest that you check the Fulton County Bureau of Vital Statistics for his birth certificate. We also suggest that you review Family Search’s website for Georgia Births and Christenings.
Since Fulton County, Georgia digital images have not been added to the Population Schedules for the 1900 Census and the Population Schedules for the 1910 Census in the National Archives Catalog, we searched Ancestry and located a Julius Miller in the 1900 Census & 1910 Census. There may be a fee associated with using Ancestry but you may access it for free at any National Archives facility nationwide using a NARA PC.
We hope this is helpful. Best of luck with your research!