From Guns.com:

The 44-page temporary restraining order halts the effective date of Senate Bill 23-169. The bill was passed earlier this year by the Democrat-controlled Colorado General Assembly and signed into law by Gov. Jared Polis, a Dem who was elected last year with the assistance of a $2.7 million campaign push by the Everytown anti-gun group. 

The law increases the threshold age to legally purchase a firearm in the Centennial State from 18 to 21, with narrow exceptions for those who are active-duty military or certified law enforcement. The lawsuit, brought by two adults aged 18-20 allied with the pro-2A Rocky Mountain Gun Owners group, challenged the constitutionality of the measure, arguing it infringed on the right to keep and bear arms.