What does the beach symbolize in the story "Through the Tunnel"?

Doris Lessing's story "Through the Tunnel" can be understood as a coming-of-age story.  Jerry and his mother are on vacation together, and Jerry is a typical, young boy.  He loves his mother, but he also wants to gain some independence from her.  He wants to test himself and see what he is capable of doing without a parent hovering right over him.  Readers realize much of this about Jerry from the first paragraph.  Jerry sees a rugged looking beach off in the distance.  It has some some rocks and is free from the crowd of vacationers, and Jerry wants to go explore it. However, he also feels badly about leaving his mother.  

Contrition sent him running after her. And yet, as he ran, he looked back over his shoulder at the wild bay; and all morning, as he played on the safe beach, he was thinking of it.

The next day, Jerry gathers up the courage to go to the other beach.  He is proud of himself, yet he does feel a bit lonely and maybe even a bit guilty at leaving his mother alone. 

There she was, a speck of yellow under an umbrella that looked like a slice of orange peel. He swam back to the shore, relieved at being sure she was there, but all at once lonely.

Jerry puts his mother out of his mind when he sees some native boys swimming in the water and diving through a long underwater tunnel.  Being able to make that swim through the tunnel becomes Jerry's sole focus for almost the rest of the story, but in order to do it, he must practice.  He cannot do that with his mother.  This is where the symbolism of the beach begins to come into play.  The tourist beach, where his mother stays, is the safe beach.  It is the beach for kids.  It is not the beach for brave teenagers and young men.  Jerry fully embraces this concept, and he even begins thinking of the tourist beach as "her beach."  His beach is the wild and rugged beach where he goes to train for his underwater swim to adulthood.  

It was a torment to him to waste a day of his careful training, but he stayed with her on that other beach, which now seemed a place for small children, a place where his mother might lie safe in the sun. It was not his beach.
He did not ask for permission, on the following day, to go to his beach.

The one beach is symbolic of childhood, safety, comfort, and security, but the wild beach is symbolic of danger, growth, adventure, uncertainty, and manhood.