I have one Amazon sword that is at least 14 years old. It has waxed and waned in sync with my interest in it, and it has fluctuated in height from 6 inches during a period of neglect to 12 - 15 inches, and back again. Its present height is 18 to 20 inches, with many leaves - too many, even.
It has thrived since I planted it in a soil substrate. Strangely (to me), it has never flowered and has only put out 2 short runners in all that time.