Correlation doesn't equal causation. Looking at the study you cited, the percent of past-month marijuana use in Colorado for 12-17 year-olds did not change significantly between 2012-2013 and 2013-2014. Also, recreational legalization went into effect in January, 2014, and using 2013-2014 data is probably too preemptive to draw conclusions on what impact legalization of recreational marijuana for adults 21 years and older has had on adolescent marijuana use.
Looking at more recent data:
"Among youth aged 12–17 in Colorado, the annual average percentage of marijuana use in the past month did not significantly change between 2002–2005 and 2014–2017."
And although not significant, past month use among 12-17 year-olds actually trended downward from an average of 10.5% in 2002-2005, to an average of 9% in 2014-2017.
It is quite sensationalist to say that 2013-2014 data showed Colorado to have the highest percent of past-month marijuana use in youth aged 12-17 and it's because of legal marijuana. It could be an outlier, as suggested by data that covers longer periods of time. Not to mention that this data doesn't tell us anything about why the percent use is what it is.
Rhode Island has had consistently higher percentages of youth marijuana use compared to Colorado, and RI has not legalized recreational marijuana.