Gray hair was scarce in the crowd celebrating at the Loop in Chicago last night. It was a microcosm of President Obama’s strengths in this election: They were young and ethnically diverse. Maybe it was the weather and the visible, although not obtrusive, presence of police, but they weren’t rowdy. They booed every state that went for Romney, but there was an air of respectful silence when Romney made his concession speech — followed by some triumphant jeering once the candidate stopped speaking and his running ate and family appeared. For this generation, the “gay issue” is settled — they cheered the passage of gay marriage measures as loudly as the roll call of states that voted for Obama.