How Old is History?

On Presidents' Day, PBS showed a new documentary about the Clinton presidency.  I heard an interview with the director on Fresh Air where he argued that the time was right for this work because it was far enough in the past that it had just become history.  Similarly, we had a candidate here a few weeks back who argued that it is appropriate to put a memorial at Ground Zero, but not a museum, since a memorial is a place for remembrance, but a museum is a place to make meaning and it was still too close to be able to acquire a deep understanding of the event.  Twenty-five years, he argued, would be necessary to achieve the temporal space needed for the required objectivity.  In both cases, there is a distinction drawn between current events, old news, and history.  Is this a meaningful distinction?  How old does something have to be to be history?