It just means that 291 years have passed in the Doctor's personal timeline since "The Impossible Astronaut". He told Amy and Rory he was 909 and he has been travelling on his own since he left Rory and Amy at their new house in "The God Complex". After this, he went on a farewell tour as he was investigating the Silence and delaying his death. This tour ended when he was aged 1103.
As the Doctor is now 1200, another 97 years have passed in his personal timeline.