According to Official Guinness Records,
The oldest person to perform a backflip is Walter Liesner (Germany, b. 14 January 1913) who was 94 yr 268 days when he performed a backflip into a swimming pool, in Wetzlar, Germany, on 9 October 2007.
Walter has been a part time gymnastics teacher for most of his life and shot to local fame aged 17 when he performed a handstand on the handrail at the top of the Wetzlar church tower, 42 metres high. He performed the backflip while filming an interview with television programme Hessischer Rundfunk.
For a complete list of 2007 records, please visit 2007 Guinness Records in Germany.