The "Description of the analyzed data set" section seems suspicious to me:
In a nutshell, young women between the ages of 14 and 17 years old
were identified and recruited by the project.
At each follow-up visit during the study period, enrolled participants
underwent STI testing and treatment. Also at each follow-up visit, the
participants received follow-up interviews, in which they were queried
about the number of unprotected coital events since previous visit.
Most of the participations did not visit the clinic every quarter and left the project before its completion.
For our analysis, we collected 1173 quarterly test results from the
first 200 participants who were never infected and have completed at
least two follow-up visits. Their average enrollment age was 15 years
with standard deviation of 1.1 years.
It means that data is biased as for some reason most of girls were not able to participate in the study.
And I'm not sure about the correctness of your interpretation. I'd interpret it as "females are 20x less likely get chlamydia infection after being treated and warned about STD" as there were relatively continuous followed-up 15-17 y/o females and no older females. And I guess it was one of the goals of this "Young Women’s Project".