This report from the CBO is more balanced and accounts for the variables you mentioned (and more). [0]
"Compared with private-sector workers, federal workers tend to be older, more educated, and more concentrated in professional occupations. To account for those differences, the Congressional Budget Office limited its comparisons to employees with a set of similar observable characteristics—education, occupation, years of work experience, geographic location, size of employer, veteran status, and certain demographic characteristics (sex, race, ethnicity, marital status, immigration status, and citizenship)—in this report"
"Compared with private-sector workers, federal workers tend to be older, more educated, and more concentrated in professional occupations. To account for those differences, the Congressional Budget Office limited its comparisons to employees with a set of similar observable characteristics—education, occupation, years of work experience, geographic location, size of employer, veteran status, and certain demographic characteristics (sex, race, ethnicity, marital status, immigration status, and citizenship)—in this report"
[0] https://www.cbo.gov/publication/60235