"My Back Pages" is a song by Bob Dylan, released on the 1964 album "Another Side of Bob Dylan". It is more widely known from the cover by The Byrds released in 1967.
Bob Dylan titles tend to very literal "Like a Rolling Stone" or very non-literal "Rainy Day Woman #12 and 35", and this is one of the non-literal ones. If you aren't familiar, this song is also
"I was so much older then, I'm younger than that now"
While some of Bob Dylan's lyrics are obscure, "My Back Pages" is perhaps his song with the most agreed upon meaning, despite its vague and poetical phrasing. This is a song about outgrowing pretentiousness and self-righteousness. After coming to fame as a protest singer, this is Bob Dylan admitting there is more to life than being an ideologue. While the specific events in Bob Dylan's life and career that the song refers to are hard to track down, of course, it is one of those songs where we know exactly what he is talking about, and it resonates decades after its release.
Also, while researching the song's release, I realize that the "younger Bob Dylan" was around 23, lamenting the strident, pretentious Bob Dylan who was...a year or two younger (older). Hearing a 23 year old castigate their 21 year old self is amusing, even if the words echoed in a much wider way.