Explanation

Option A is correct: In the Gupta period, Vishti (unpaid forced labour) was recognized as an institutionalized form of state exaction. It was treated as a legitimate source of state revenue, functioning as a labor tax paid by the subjects in lieu of cash or grain taxes to build embankments, dig canals, and support military logistics.

– Option B is incorrect: Epigraphic land-grant copper plates from the Malwa (Madhya Pradesh) and Kathiawar (Gujarat) regions regularly list vishti among the customary levies and state prerogatives remitted to donees.
– Option C is incorrect: Vishti was an unpaid, compulsory levy; laborers were not entitled to statutory weekly wages.
– Option D is incorrect: There was no customary or statutory rule dictating that specifically the eldest son had to be dispatched for forced labor.

Therefore, the correct statement is Option A.