As the joke goes: "If you remember the 60s, you weren't there".
"Mellow Yellow" was a single by Scottish folk-rocker Donovan, released in October of 1966. The lyrics are a lyrically celebration of being a laid-back dude, and were misunderstood at the time about smoking banana peels. Apparently, the line about an "electrical banana" referred to the new availability of vibrating dildos. And the line about "I'm quite mad about fourteen" might be about something quite unsavory.
Back to the 1960s and remembering them: I was born in 1979, which means I remember the 1960s quite well. In my memory of the 1960s, there was a brief period, basically less than a year, around 1966, when British Invasion groups singing about romance dabbled in psychedelia before everything broke open into psychedelia and hard rock. And to me, Donovan was a pop singer who wrote accessible songs who was briefly popular before Jimi Hendrix changed everything. "Mellow Yellow" went to number two in the charts, and with its singalong chorus and easy rhymes, it seemed to be almost a bubblegum song. "Sunshine Superman" had been a #1 single, and "Mellow Yellow" got to #2. It also represented the peak of Donovan's career, as the nascent "electric folk rock" would split into either easy listening or hard rock.
But this is all in retrospect. At the time that "Mellow Yellow" came out it wasn't a novelty song from a brief gear shift in the history of music. At the time it came out, Donovan was a pioneer who was being mentioned as the British Bob Dylan. To me, listening to this song now, I can hear an unrealized direction that music might have taken.