**Core Concept**
Pilocytic astrocytoma is a type of slow-growing, benign brain tumor that primarily affects children and young adults. It is a grade I astrocytoma, characterized by its distinct histological features and relatively favorable prognosis.

**Why the Correct Answer is Right**
The correct answer is incorrect because pilocytic astrocytoma typically presents in children and young adults, with a median age at diagnosis ranging from 5 to 15 years. This age range is significantly lower than 80 years, making option D an incorrect statement. Pilocytic astrocytomas are more common in children due to the high proliferation rate of astrocytes during childhood and adolescence.

**Why Each Wrong Option is Incorrect**
**Option A:** Long survival is a characteristic of pilocytic astrocytoma due to its benign nature and slow growth rate. Patients with complete resection of the tumor often have an excellent prognosis.
**Option B:** Total surgical resection is indeed possible and often the primary treatment for pilocytic astrocytoma, especially in cases where the tumor is completely encapsulated and easily accessible.
**Option C:** Pilocytic astrocytoma can indeed involve the posterior fossa, a common location for this type of tumor. The posterior fossa is a critical area that contains vital brain structures, and tumors in this region can cause significant clinical symptoms.

**Clinical Pearl / High-Yield Fact**
A key characteristic of pilocytic astrocytoma is its distinct histological appearance, featuring Rosenthal fibers and microcysts. These features are essential for the diagnosis of this tumor type and should be recognized by pathologists and clinicians alike.

**✓ Correct Answer: D. Median age at presentation is more than 80 years**