Are there any group queue restrictions in competitive?
Yes.
In order to queue with friends, there are certain criteria:
You must be at least level 25.
Your account must not be banned.
You must be within 50 Skill Rating of your friends. Skill Rating is a 100 point scale, and your initial rating is determined by 10 Placement matches at the beginning of each season.
Source
For Overwatch Competitive Play, as of Season 2:
- For Bronze through Diamond ranks players must have a skill rating within 1000
- For Master and Grandmaster ranks players must have a skill rating within 500
Ranking groups are provided in the chart below