  Earth will become uninhabitable within 2-3 Gyr as a result of the moving
boundaries of the habitable zone caused by the increasing luminosity of the
Sun. Predictions about the future of habitable conditions on Earth include a
decline in species diversity and habitat extent, ocean loss and changes in the
magnitudes of geochemical cycles. However, testing these predictions on the
present-day Earth is difficult. The discovery of a planet that is a near
analogue to the far future Earth could provide a means to test these
predictions. Such a planet would need to have an Earth-like biosphere history,
requiring it to have been in its system's habitable zone (HZ) for Gyr-long
periods during the system's past, and to be approaching the inner-edge of the
HZ at present. Here we assess the possibility of finding this very specific
type of exoplanet and discuss the benefits of analysing older Earths in terms
of improving our understanding of long-term geological and bio-geological
processes. As an illustrative example, G stars within 10 parsecs are assessed
as potential old-Earth-analogue hosts. Surface temperature estimates for
hypothetical inner-HZ Earth analogues are used to determine whether any such
planets in these systems would be at the right stage in their late-habitable
lifetimes to exhibit detectable biosignatures. Predictions from planet
formation studies and biosphere evolution models suggest that only 0.36% of G
stars in the solar neighbourhood could host an old-Earth-analogue. However, if
the development of an Earth-like biosphere is assumed to be rare, requiring a
sequence of low-probability events to occur, then such planets are unlikely to
be found in the solar neighbourhood - although 1000s could be present in the
galaxy as a whole.
