Grey Squirrels have an average lifespan of around 12 to 14 years in the wild.
But when Grey Squirrels are kept in captivity then they can live up to 20 years.
The reason Grey Squirrels have a much shorter lifespan in the wild versus in captivity is that when in Captivity is due to predation and other challenges in the squirrels habitat.
Also the squirrels could get run over or killed in other ways out in the wild so that also shortens their lifespan.