There is no magic birthday when a man should hand over the toolbox. A 60-year-old who moves confidently on a ladder may handle a job safely, while a 45-year-old with poor balance should think twice before reaching for the roof.
The better question involves ability, risk, and recovery. A repair that once took an hour may become a bad bargain if one slip can lead to weeks of limited mobility, medical bills, or a long interruption to everyday life.