I really like this Japanese rap song, but you need to understand Japanese to appreciate it.
Basically the first verse is a kid on the playground talking about playing catch, his friends liking girls, and other childhood things. The chorus is him saying lets all play together forever, even when we're adults.
Second verse is a more grown adult in his 20s - talking about recording in the studio, having fun with his friends, on stage at the club, and "playing" everyday being his dream.
Final verse is a more grown adult in his 30s - talking about how time flies, his friends' jobs, those who've become fathers, others who've gained weight, and those who passed away (reference to his father who committed suicide when he was a kid) - saying one day they'll meet again.
The song is super nostalgic, I think especially for me since I actually spent some of my childhood in Japan.
It's a bit melancholic for me as well. There was a purity to childhood. But then after school you get thrust into the wild and have to make money. Some are able to make a living do what they love, but most can't - slaving away at jobs they have zero passion for for a paycheck (reminds me of this classic Steve Cutts video). After university it becomes exponentially harder to make friends (unless one makes a conscious effort to), connections drift apart, people get into serious relationships and drift even further apart. The carefreeness of childhood turns into responsibilities, work, bills, stress, kids, etc. "Playing" and socializing becomes less frequent, with social interactions more resembling "networking" or "what can you do for me", and serious, distant conversations.
Of course that's a pessimistic take. There are great things about being an adult as well, and ultimately life is what you make of it. I think it's common for people to say that their childhood years were their best. But I will not resign to my best years being in my past, and will always strive to live to the fullest even into old age - always trying to keep that childhood playfulness, carefreeness, and curiosity.