Paramedics performed CPR but he could not be revived, news.com.au reported.
His parents Raymond and Jeanette Zimmerman released a statement on their son's death.
"It is with deep sorrow and heavy hearts that we share the news of our son's passing from this earth to return home to his Heavenly Father," they said.
Mr Zimmerman had been working for the church's Sydney mission since 2017.
"He was a great example to us all, and he loved his mission very much. He enjoyed teaching people and sharing the gospel of Jesus Christ," his parents said.
"Gavin was a bright light in our lives."
Sutherland Mayor Carmelo Pesce told the ABC that he had been briefed by senior staff and told that police had recovered a phone with photographs of the teenager taken moments before he fell.
"I've been told that the police have recovered a phone that has photographs on there of the young gentleman taking photos and he was extremely close to the edge of the rock," he said.
Chief Inspector Chris Hill urged anyone visiting the area to take extra heed of warning signs at the lookout.
"Those rocks are very slippery. For your safety, we recommend that you stay up on the whale watching platform and please don't go down on the rocks," he said.
He said early investigations suggested it was a case of misadventure.
"It would appear at this time he was here with a group of friends to go whale watching," he told reporters at the scene.
"They've made their way down to the rock platform … He's slipped and fallen over the edge and unfortunately died."
