https://www.yahoo.com/lifestyle/teen-marijuana-rise-increasing-10-153828763.html
From June.
https://www.washingtonpost.com/national/potent-pot-vulnerable-teens-trigger-concerns-in-first-states-to-legalize-marijuana/2019/06/15/52df638a-8c9a-11e9-8f69-a2795fca3343_story.html?utm_term=.f72b35be3a96
145 days ago:
https://psychcentral.com/news/2016/12/27/marijuana-use-up-among-teens-since-legalized-in-colorado-washington/114378.html
Right now pot is not only legal but has less of a social stigma then even drinking does. OF course there will be more teens doing it.
BTW I would discount ANY reports commissioned by the state of Colorado. They will never tell the truth about use among teens or else they'd have to admit there's a problem with legalization.
From the second article you linked...
“The study, published in JAMA Pediatrics, showed that legalization of recreational marijuana use significantly reduced perceptions of marijuana’s harmfulness by 14 percent and 16 percent among eighth and 10th graders and increased their past-month marijuana use by two percent and four percent in Washington state, but not in Colorado.”
And the first article you posted makes NO assertion of increased use by teens.
And the newest data is what's reported in the article at the top of this thread - so there you go.