The lyrics describe a boy who is feeling anxious about his own future when he will no longer be a teenager, pondering such questions as "Will I love my wife for the rest of my life?"

"When I Grow Up (To Be a Man)" was composed by Brian Wilson with lyrics by both him and his cousin and frequent writing partner Mike Love.

As I look back on that I am happy with my life now and I didn't think I would be.”[3][4] In his 2016 memoir, Love wrote that the song was "probably influenced" by Murry Wilson, who constantly challenged Brian's manhood.

"[11] "When I Grow Up" features multiple key changes, a hook based on a dissonant, functionally ambiguous chord, tempo stretches, and a long pause as a climax.

[12] O'Regan brought special attention to the drum pattern for avoiding a traditional backbeat rhythm common to rock and roll songs of this era.

In his book Inside the Music of Brian Wilson, Lambert writes that this unusual chord "grabs our attention immediately."

The instrumental track was recorded on August 5 with a basic line-up of Brian on piano, Carl on guitar, Al Jardine on bass, and Dennis on drums.

[18] During the band's first British tour in November 1964, they performed this song for their first television appearances in Britain, on Discs a Go Go, The Beat Room, Top Gear, and Ready Steady Go!.

[24] An a cappella mix of the song was released in 2014 on the compilation album Keep an Eye on Summer – The Beach Boys Sessions 1964.

Upon its initial release, Cash Box described it as being in "jumpin' rhythmic manner that has made [the Beach Boys] such big teen favorites.

Harrison also compares it to its B-side "She Knows Me Too Well", nothing that both feature "complex lyrical expressions" of "un-fun topics"[29] In a list ranking the Beach Boys' 50 greatest songs, Mojo magazine placed it 39th, describing it as "an ode to youth's fleeting nature.

[31] Surviving sessions audio and AFM musician contracts sheets, documented by Craig Slowinski have enabled this personnel list to be compiled.