I was working with Kame's radio show timing when I came upon this song by Angela Aki: Tegami - Haikei Juugo No Kimi E.
Kame was talking about this song before he broadcast it on his show, and it is about a 15-year-old who writes a letter to her future self.
....
Actually, I did that once. But I was twenty and I wrote to my 25-year-old self. Now, where did I put that letter...? XDD
Somehow, it gives a nostalgic feeling. Past times, lost times... memories, you know. ^^;
Anyway, this song is really beautiful, so please listen to it....
(Click on the Japanese song title!)
手紙 ~拝啓 十五の君へ Edit: Found a video with Angela Aki. She is the same age as me. XD
Lyrics
here for those interested, with romaji and translations.