Most ninjas probably don't live very long by the nature of their work. They die on missions, in wars, in raids, while being ambushed by other ninjas, during testing, etc.
However, the handful of ninjas we have seen (e.g. The Third Hokage, as well as Tsunade and Jiraiya) who've lived past the usual lifespan seem to be of very advanced age.
Do ninjas have a longer natural lifespan that is simply cut short by the nature of their work?