Reading between the lines, I believe your father's condition is due to a bicuspid syndrome. The aorta valve has two cuspids (flaps that close the valve opening) instead of the normal 3 cuspids.
The condition is congenital and as an individual reaches the age of thirty-five and greater, some individuals with the syndrome have a problem with the aorta increasing in size. When the size is increased to 5.0 or more (begin the watch and wait), there becomes the risk that the aorta could rupture and surgery may be necessary to prevent dissection (can be fatal). During surgery sometimes the valve can be saved and sometimes valves need to repaired or replaced. Favorable outcome is expected, and the risk is low.
To delay an operation for 4-5 months may not be unreasonable as growth is about 0.5 cm per year if I remember correctly, but your father's history on time/size increase may be known by the doctor.