**Core Concept**
A Colles fracture is a type of fracture at the distal end of the radius bone in the forearm, characterized by a displacement of the bone fragments. This fracture typically occurs due to a fall onto an outstretched hand, resulting in a fracture at the cortico-cancellous junction.

**Why the Correct Answer is Right**
The correct answer, **D. Garden spade deformity**, is incorrect because a Colles fracture typically presents with a dorsal angulation and displacement of the distal fragment, resulting in a characteristic "dinner fork" deformity. The Garden spade deformity is not a characteristic feature of a Colles fracture. The cortico-cancellous junction is the correct location of a Colles fracture, which is why option C is correct. Colles fractures are indeed more common in older adults, making option A correct as well. Option B, dorsal shift, is also correct as it describes the typical displacement of the distal fragment in a Colles fracture.

**Why Each Wrong Option is Incorrect**
**Option D:** The Garden spade deformity is not a characteristic feature of a Colles fracture. Instead, a Colles fracture typically results in a "dinner fork" deformity due to the dorsal angulation of the distal fragment.

**Option A:** This option is incorrect because it contradicts the statement. A Colles fracture is indeed more common in old age due to decreased bone density and increased risk of osteoporosis.

**Option B:** This option is incorrect because it is a characteristic feature of a Colles fracture. The dorsal shift of the distal fragment is a common displacement seen in this type of fracture.

**Option C:** This option is incorrect because it contradicts the statement. A Colles fracture typically occurs at the cortico-cancellous junction, making this option incorrect.

**Clinical Pearl / High-Yield Fact**
A Colles fracture often results in a characteristic "dinner fork" deformity due to the dorsal angulation of the distal fragment, which is a key feature to identify on clinical examination.

**✓ Correct Answer: D. Garden spade deformity**