Treatment of benign tumor of pelvic bone of74 years old patient?

Depends on the tumor. Some tumors can cause pain or have a risk of fracture, in which case treatment with surgery may be needed. Most benign bone tumors can simply be observed.
Supportive. What kind of benign tumor of pelvic bone you are referring here? Observation and supportive care, in general , would be the recommendation for a benign tumor- unless- if it starts causing significant problems- then perhaps other procedure may be considered. Please discuss further with the doctor.