The full article is linked [1] and I can view it. See Fig. 1 and quoting the actual article:

"Specifically, 28.8% of adolescent men ages 14–17 were categorized in Class 2 (no sexual behaviors) in 2009 compared to 44.2% in 2018. Among adolescent women, 49.5% were categorized in Class 2 in 2009 compared to 74.0% in 2018."

For adults the percentage was much lower -- 3.8% rising to 3.9%.

[1] https://link.springer.com/article/10.1007/s10508-021-02125-2