Most children with autism are well past their fourth birthday by the time they’re diagnosed with the condition, according to new government data. Their parents and teachers may have raised red flags earlier, but it takes months or years to confirm suspicions with a formal diagnosis. And therapy rarely starts without one. “The school wouldn’t do anything for us until we had a diagnosis,” said Kimberly Vincent, of Wallingford, whose daughter Rebekah was diagnosed at age 6. That’s why researchers are trying to come up with new strategies for diagnosing autism spectrum disorders as early as possible. Last month’s release of new government data showing autism spectrum disorders now affect one in 68 kids provided an extra push and sense of urgency, several experts said.