Things change, people evolve or sometimes they don’t. This is very fertile ground to write about. Getting married, puberty, getting divorced, getting sick, death, getting a new job, getting fired, getting dumped, dumping someone, etc, etc, etc. Also remember this is just a prompt to get you started, write about whatever you want.
King Gizzard and the Lizard Wizard - Catching Smoke
This song is from an record called Butterfly 3000 and it’s all about change. In the video he changes from a chrysalis to a butterfly. The dancing after the change is amazing at around 4:17.
This song started as themed but morphed lyrically into something else. You gotta go with the artistic flow, so not themed. Once I stopped trying to force it things flowed a little more. There's still some bits that I want to change: rerecord the chorus so that "Grace" is changed to "Lord" and maybe have the chorus become a bridge and create a new chorus.