Following up on the common practice of Thai boys entering monkhood.
I found this link which says it is common practice, but for 20-year-olds.
The cave boys were nowhere near 20 years old.
they were kids, not adults.
https://www.thaiwaysmagazine.com/thai_article/2407_buddhist_monks/buddhist_monks.html
https://www.cbsnews.com/news/thailands-rescued-cave-boys-complete-their-time-as-novice-buddhist-monks-2018-08-04/