It is important to understand that viruses don't actually live.
They are simply DNA or RNA material encased within a protein
complex (a virion). They cause damage when they come in contact
with a host's cells and are able to attach and take them over to
replicate themselves using the host's energy and materials. A more
appropriate question might be how long can a virus stay airborne?
This can be answered if the size of the specific viral organism is
known and how much weight it has to affect the ability of the
respiratory droplet containing it to stay afloat on air currents
produced by the cough or sneeze. Usually, especially for cold and
flu viruses, this is only a matter of seconds and for a diameter of
six feet from the person who coughs or sneezes and produces the
respiratory droplets, otherwise, they fall from the air to land on
surfaces in that approximate 6 foot area.
They can remain active (e.g., able to infect someone) for longer
on the surfaces and on objects that receive the droplets as they
fall from the air. Often, for flu and cold viruses, this is around
48 hours, but does vary as noted above according to the size of the
individual virions. See the related questions below for more