The song was written within three days in Los Angeles, after Adele struggled with writer's block during unfruitful early sessions for the album.

Adele performed the song during her television specials, and at Saturday Night Live, The Ellen DeGeneres Show, and the Brit Awards 2016.

"[2] Adele struggled with writer's block and her manager, who was also unsure about the material, asked Rick Rubin, a producer of many songs on her sophomore studio album 21 (2011).

[3] In early 2015, she flew to Los Angeles to work with new songwriters and producers for two months, including Canadian musician Tobias Jesso Jr.,[3] after discovering his song "Hollywood".

"[7] American record producer Ariel Rechtshaid heard rumours that Adele and Jesso wanted to work with him.

Rechtshaid told The Fader that it only took two takes to record the song, and during the middle eight, he pushed Adele beyond her means, since he "felt that it needed to have a little bit more cry to it".

[10] On 26 November 2015, Billboard wrote an article questioning what would be 25's next single, indicating either "When We Were Young" or "Send My Love (To Your New Lover)" would be their pick.

[4] It is built around "somber piano chords", which according to Pitchfork's Jeremy Gordon, are "designed to show off [Adele's] staggering, empathic voice".

[25] The song "finds [Adele] reconnecting with [an] old acquaintance years after their adolescence, which prompts her to revisit those memories and to wish she could stop time".

Gordon named it "Best New Track" and praised Adele's vocal performance and how she was "capable of elevating maudlin sentiment into high art".

[23] Stephen Thomas Erlewine of AllMusic selected the song as one of the album's highlights, noting that she took a risk enlisting Retchshaid to produce the track.

[30] Leah Greenblatt from Entertainment Weekly considered it one of the three best tracks of the album, noting that she was sincere with the nostalgic theme.

[32] Rob Garratt from The National was positive about Adele's writing skills, and praised her "fragilely affecting, but ultimately affirming" performance.

[33] Writing for Inquirer, Joseph R. Atilano remarked, "A single like this further showcases how lyrically intelligent she is as a composer as well as one of the greatest pure singers alive today.

[38] Jon Dolan from Rolling Stone labelled the song a "mature [...] torchy ballad",[39] while T. Cole Rachel of Spin defined it as "the kind of mawkish, overcooked melodrama that one imagines Adele could perform in her sleep".

[40] Chris Gerard from PopMatters was praiseful, naming the song "a bittersweet epic", and adding, "'When We Were Young' is breathtaking, an example of how great Adele can be when all the stars align.

Rolling Stone listed it as Adele's fifth-best, and Larisha Paul elaborated that "she spins the existential crisis-inducing topics of time and aging into what feels like a snapshot of our own past, present, and future".

[47] "When We Were Young" peaked at number nine on the UK Singles Chart and received a 3× Platinum certification in the United Kingdom from the British Phonographic Industry (BPI).

[52][53] In Australia, "When We Were Young" peaked at number 13 on the ARIA Top 50 Singles Chart and the Australian Recording Industry Association certified it Platinum.

[72] Adele performed "When We Were Young" live with numerous backup singers, afront large speakers, at The Church Studios in London, which was filmed and uploaded to Vevo on 17 November 2015.

[73] Adele sang it on Saturday Night Live on 21 November 2015; MTV News' Renan Borelli commented that she "absolute[ly] crushed [it]".

[84] Colin Stutz of Billboard stated she "put her vocal chops on full display" and justified her place on the list "of the best singers in pop music".