Yes, if I loved it and it wasn't a physical strain. Working 40+ hours at age 80 is likely to become a strain for most people. However, I know a bicycle shop owner still running his small shop, alone or with part-time employees. He still bikes and is in great shape as well. Writers and painters often go past 80, too. Some teachers and preachers do so as well.
The body generally cannot handle the persistant strain if great physical effort is required. Some careers can evolve around typical ailments and slowdown, but not all.