A 72-year-old man is found incidentally to have corrected serum calcium of 2.90 mmol/L (2.10-2.60) on routine bloods. He is asymptomatic. Repeat testing confirms hypercalcaemia and shows raised parathyroid hormone (PTH) with normal renal function and no vitamin D deficiency. According to consensus guidelines, which of the following features would most strongly support recommending parathyroidectomy for primary hyperparathyroidism?