Some people don’t know when to quit, and sometimes that’s a good thing. Violinist Robert Mann, founder and long-time first violinist of the Juilliard String Quartet is now in his nineties. And he’s founded a new quartet, the Mann String Quartet. The other members of the quartet are all children of Juilliard Quartet members — including Mann’s son, Nicholas, on viola. The debut recital happens at the Community Music Center on April 5. Hey, it’s a family thing, but you’re invited. How often does that happen?