How is Jerry swimming through the tunnel a symbol of his rite of passage into adulthood?

Jerry sees the beach as "a place for small children, a place where his mother might lie safe in the sun." Rather than stay with the children, he chooses to leave the safety of the beach and journey to the treacherous "wild and rocky" bay and the underwater tunnel. At eleven, Jerry in entering puberty, he is fatherless and approaching adulthood.... he will one day be the man of the house. Throughout the story, he and his mother sometimes engage tense conversations.

Jerry considers conquering the tunnel to be a rite of passage into adulthood. He must venture into the wild, brave the elements, and face the dangers of the world alone. When he finally achieves his goal, he returns to his mother and proudly declares that he "can stay underwater for two minutes-three minutes at least." This statement belies the danger he has faced and insures the secrecy of his personal rite.