Urashima Tarô, the legend

Urashima Tarô is one of the most known japanese stories, it is about a young fisherman called Tarô. I saw pictures and drawings of him, and I was interesed for this legend, so I was searching information and I think that is very intersting, I really like the story. I'm going to explain it:

One day, Taro was fishing when he saw a little boys tormenting a small turtle, he saved the turtle and let it go back to the sea. The day after this, another turtle appeared and told him that the litlle turtle was the daughter of the Emperor of the Sea, and the Emperor wanted to thank him, then, the turtle gave (magically) gills at Taro, and brought him to the bottom of the sea, to the Palace of the Dragon God. The little turtle was now a beautiful princess, and he stayed in the Palace for a few days. Then, he wanted to go back for saw his mother, and the princess was agree, but she gave him a mysterious box which she told him never to open. Taro leaves again with the turtle.
When he arrived, everything was changed: 300 years had passed since the day he had left for the bottom of the sea. He was very angry and opened the box. Sudenly, a white smoke come out of it, and he became an old man. He heard the voice of the princess.. "In the box was your old age, I told you not to open it..."
The final of the story is open, there's many versions, for example, in a version he ate a magic pill that gave him the ability to breathe underwater. In another, he is swept away by a storm before he can rescue the turtle. There is a version in which he dies in the process of aging, as no one can live 300 years.