Paternal age at time of reproduction accurately predicts mutation rates in a range of species from owls monkeys to humans and beyond.
The theory is simple. Mutations accumulate at a certain rate per year, starting at the age of sexual maturity, and the longer a father lives after sexual maturity but before a father has children, the more time there is for mutations to accumulate in germ line cells. Thus, a species that reproduces on average two years after sexual maturity is going to have fewer mutations than one that reproduces at age ten years after sexual maturity, which in turn will have fewer mutations than one that reproduces at thirty years after sexual maturity.
The study in question uses the mutation rate in owl monkeys to accurately predict the mutation rate in chimpanzees and humans for a given paternal age with only this very simple model.