Programmers see a simple age calculation and immediately apply the most straightforward algorithm: current age minus the age difference. Meanwhile, testers are out here considering every edge case from relativistic time dilation to family affairs.
This is why we can't ship on time. Devs think they're done after the happy path works, while QA is busy writing test cases for "what if your sister is secretly an astronaut experiencing time dilation" scenarios.
And this, friends, is the eternal dance between developers and testers that's been keeping software barely functional since the dawn of computing.