How common are brain tumors in a 23yo female?

Quite rare: Approximately 4 people out of 100,000. To compare: the likelihood of dying in an automobile accident in the United States is 11 people out of 100,000.

Rare: There are two peaks to the incidence of malignant brain utmors. The first such peak is in children under the age of 15 and then there is a later peak in the mid 70's. The most common brain tumor in a 20 year old female would be one of the bening tumors such as meningioma, schwanoma or pituitary adenoma. The overall incidence for all types of brain tumor in a 20 year old would be ~8/100,00

Talking Dinosaur: How about some symptoms to comment on to see why you are thinking in terms of brain tumors which are likely as common as TALKING DINOSAURS? In the UK statistics suggest that tumors of the NERVOUS SYSTEM EN TODO (i.e. brain/spinal cord/etc) come out to about 90 cases PER YEAR or 7.5 cases/100,000 population. Also, remember, not all tumors are malignant so TALKING DINOSAUR's the phrase of the day!

Not common: the twenty three year old woman is beyond the pediatric stage but there are some tumors that are more common in younger women. These include a form of medulloblastoma that seems to have a better prognosis in this age group. The type of tumor is very important as it relates to outcome. Glioblastoma, luckily is rare in this age group and has a worse prognosis.