By comparison, in 2010, the over-70s prison population was 629.
The surge in numbers comes as more people who committed crimes decades ago are now being brought to justice.
Much of the rise is said to be down to the so-called Sir Jimmy Savile effect, where victims are now more willing to come forward to speak about the abuse they suffered many years ago.
Celebrities, religious figures and schoolteachers are among those now being held to account.
Ralph Clarke is believe to be the older person convicted in British legal history (Image: PA)
Police forces are pumping more resources into these types of investigations to ensure people are brought to justice, even if the crimes were committed 20, 30 or 40 years ago.