Answer :
actually when he used 2 be young he used 2 climb trees effortlessly,but as he grew older his capability decreased.So he said it was my youth.
He meant that he had grown older and now he didn’t have energy like young child to climb the tree. In this story, Mr., Bond came back to his city named Dehra where he spent his childhood days. He was remembering all the childhood memories and old days in that place where he was youth once. While seeing a familiar tree a young boy came and asked why he was staring at the tree than Bond explained how he loved that jackfruit tree forty years ago and placed a crossed on it. When boy asked him to climb that tree and looked for that cross, Bond knew he was no more a child of that era.