know the answer to this, because promoting/concert booking is a career path I'm actually working towards & looking to get into. I'm trying to jog my brain here... I believe I asked a guy in charge of a large venue about why some shows have age limits and such, and he said it's the concert promoter who decides that.
The Grouplove concert in Rochester is promoted by After Dark Entertainment. My friend is an intern with them right now, and I'm trying to intern with them next semester. They seem like a really cool company. Call them, and ask them your question specifically.
Here is their website, and their contact info is right there in the box on the top right:
Hope that helps. Seems like it would be a good show!