The Old Man in the title is the name of the shrub the cache is hidden in or on - Old Man Banksia or Banksia serrata.The Banksia shrubs were named for Joseph Banks who was the botanist on Captain Cooks 1770 voyage.
The shrub is located next to the fabulous mural which adorns the concrete wall that surrounds Sutherland's water reservoirs.
Look for the kangaroo in the mural .The shrub is nearby.