Fitness for surgery at 78 years age depends on the present condition of patient.
Many elderly people are active into 80s and 90s and are even holding responsible positions in public and corporate life.
Next Steps
You can always take second or third opinion from reputed Neurosurgeons in your area.
Health Tips
Ultimately, the decision to go for surgery or not in a case of brain tumor is an intensely personal decision.
It also depends on how dangerous the brain tumor is.
Please share the MRI reports for further guidance. Images are better as "a picture speaks a thousand words".