According to Official Guinness Records,
The record for the oldest documented age for a donkey belongs to Suzy, who reached 54 years old in 2002. Suzy was owned by Beth Augusta Menczer (USA) and lived in Glenwood, New Mexico, USA. Suzy died in 2002, during her 54th year.Suzy was originally bought in 1949 as a yearling (thus born in 1948) and lived on Moon Ranch, New Mexico until 1968. Suzy was bought by her current owner in 1973, who had her checked by a vet. The vet placed her age at 21 or 22 years old, meaning she would be 50 in 2002. Ms Menczer traced Suzy's records and previous owners who attest to her being 1 in 1949. The average life span of a donkey is 25-30 years.The record was updated and altered from 'oldest donkey living'.
For a complete list of 2002 records, please visit 2002 Guinness Records in United States.