Saw my first "Nodo Jiman"（のど自慢）in a few weeks. One indication that the old kayo ought to be lasting for a good while longer is seeing some of the young kids performing it on stage. I saw a 13-year-old boy singing the tune of this article less than an hour ago, and although he didn't get the full triumphant barrage of bells, he still got a thumbs-up from me. He wasn't totally on tune but it was because of that, he probably got the lion's share of accolades.
The song in question was "Utsukushii Juudai" (The Beautiful Teens) as originally sung by Akira Mita（三田明）. It's been included in that sub-genre known as seishun kayo（青春歌謡...salad day pop music）with all of those nostalgic stories of high school life. I believe Kazuo Funaki's（舟木一夫）"Koukou Sannen-sei"（高校三年生）would be the quintessential example of such a song.
According to J-Wiki, "Utsukushii Juudai" was the debut single of Mita who became popular for his innocent looks and wonderful voice. Released in November 1963, the song was written by Tetsuo Miyagawa（宮川哲夫）and composed by Tadashi Yoshida（吉田正）, and focused on that adorable young love during those tender if sometimes turbulent time in life. Couldn't get more musically sepia than those strings and backup chorus.
A few months after the release of the single, its success meant that a movie with the same title was produced with Mita taking on a supporting role.
Mita was born Ushio Tsujikawa（辻川潮）in Tokyo in 1947. In 1962, while appearing on the NTV music variety program "Ajinomoto Hoihoi Music School"（味の素ホイホイ・ミュージック・スクール）, composer Yoshida took the young Mita under his wing, and several months later, the singer and actor made his debut. At the time, the Gosanke（御三家...The Big Three）trio of Yukio Hashi（橋幸夫）, Teruhiko Saigo（西郷輝彦）and the aforementioned Funaki were the singing heartthrobs but although Mita was seen as being a Johnny-come-lately to the proceedings, the media did place him with those three, thus having the quartet dubbed as the Shitennou（四天王...The Four Heavenly Kings）.
It looks like Mita's heyday was the 1960s which was punctuated by his 6 straight appearances on NHK's Kohaku Utagassen. However, he never sang "Utsukushii Juudai" during that run between 1964 and 1969.