**Core Concept**
Pilocytic astrocytoma is a type of slow-growing brain tumor that arises from astrocytes, a subtype of glial cells. These tumors are common in children and young adults, and they often occur in the posterior fossa, which is the region at the base of the brain.

**Why the Correct Answer is Right**
The correct answer is incorrect because pilocytic astrocytomas typically present in children and young adults, with a median age at presentation of around 10 years. This is due to the slow growth rate of these tumors, which allows them to accumulate and become clinically significant over time. The tumors often occur in the posterior fossa, particularly in the cerebellum or brainstem.

**Why Each Wrong Option is Incorrect**
**Option A:** Long survival is indeed true about pilocytic astrocytomas, as they are generally slow-growing and responsive to treatment. This is a key characteristic that distinguishes them from more aggressive types of brain tumors.

**Option B:** Total surgical resection is often possible for pilocytic astrocytomas, especially if they are well-circumscribed and located in accessible areas of the brain. This is one of the main reasons why these tumors have a relatively favorable prognosis.

**Option C:** Pilocytic astrocytomas can indeed involve the posterior fossa, which is a common location for these tumors. In fact, the cerebellum and brainstem are frequent sites of origin for pilocytic astrocytomas.

**Clinical Pearl / High-Yield Fact**
A key clinical characteristic of pilocytic astrocytomas is their tendency to occur in children and young adults, often presenting with symptoms such as headaches, vomiting, and ataxia. These tumors are generally slow-growing and can be cured with surgical resection, making them a relatively favorable type of brain tumor.

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