Jurors found Ralph Clarke from Erdington, Birmingham, guilty of 21 counts of abusing two girls in the 1970s and 80s.
He admitted nine charges relating to a young boy part-way through his trial at Birmingham Crown Court.
Clarke told police he was "immune to feelings", the court heard.
The former Royal Air Force serviceman, of Holly Lane, who was born in March 1915, sat impassively as the unanimous verdicts were delivered, the BBC reported.
Judge Richard Bond said he needed to "ponder with care" the sentence and added: "The reality is that he's so old it's unlikely he'll be released back into the community."
At the start of Clarke's trial, prosecutor Miranda Moore said the defendant was arrested after two of his victims walked into a police station in August last year.
Detective Con Emma Fennon from West Midlands Police's historical sexual offences team described the crimes as "horrific offences" and said Clarke showed no remorse.
When questioned on the merits of taking a 101-year-old man to court, she said: "The day that not prosecuting someone who hurts a child is not in the public interest, we may as well all pack up and go home."
She said: "The nature of what he did to his victims has robbed them of their childhood."
Claire Nicholls from the West Midlands Crown Prosecution Service said for more than 40 years "Clarke thought he'd got away with his crimes".
"However, due to the courage of the victims we were able to bring this defendant to justice," she said.
His victims reported the offences to West Midlands Police in August last year after seeing Facebook posts celebrating Clarke's 100th birthday.
Investigations revealed a catalogue of abuse spanning many years, the report said.
The retired lorry driver was remanded in custody and is due to be sentenced on Monday.
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