But Douglas Hammersley, who will turn 102 this month, has been spared jail for molesting his young victim during the 1970s.
The woman, now in her 40s, went to the police after his family threw him a party for his 100th birthday last year and the event was reported in a local newspaper.
She was praised for her bravery and courage during the sentencing hearing at Aylesbury Crown Court on Monday.
Hammersley, who was excused from attending, was given a two-year suspended prison sentence, placed on the sex offender register and ordered to pay £25,000 compensation.
Judge Francis Sheridan said: "To award compensation is wholly unusual in a case like this but the young victim has carried this cross of abuse for year upon year upon year.
"She very properly complained to anyone that would listen.
"She has waited a very long time for justice but I hope justice is what