It normally takes 18 years to advance from step 1 to step 10 within a single GS grade if an employee remains in that single grade.
https://www.opm.gov/policy-data-oversight/pay-leave/pay-systems/general-schedule/
https://www.youtube.com/channel/UC73YiDw_qGypmjQ2NSkugGw
저라면 GS-13을 택할 것 같네요.
Good Luck!!