角の丸い棘 literally means “a thorn with rounded edges,” creating a striking image of something that looks sharp but can no longer pierce.
In the song, it describes how rebellion or resistance has been softened with age, suggesting that a person who has lost their edge cannot make a real impact. This unusual poetic phrase is memorable because it turns inner conflict into a vivid physical image.
"AGE" is Janne Da Arc picking a fight with growing up. The singer opens by telling someone to stop lecturing him from on high: お説教はやめてくれ (stop the sermon), and then shrugs it off with 俺はバカだからわからない (I'm an idiot, so I don't get it). 屁理屈 (herikutsu) is a great word to learn here: it means hair-splitting, quibbling logic, the kind of argument that is technically clever and totally useless.
Then the bravado cracks. He admits he has lost 出口と武器 (the exit and my weapons), and that lately he has even gotten good at fake smiles, 作り笑い. Back when he was fearless he had nothing to lose; now that he knows the fear of losing, he is at a fork in the road, 分かれ道. The chorus is his answer: ジャッジをくだせ (hand down the verdict), stop lying to your own heart, and if it's worthless, すべて捨ててしまえ (throw it all away). If people laugh and call him a brat, ガキ (a rude word for a kid), then fine: 大人にならなくていい (I don't have to become an adult).
My favourite image is the self-roast in the second verse: 角の丸い棘 (a thorn with its corners rounded off) can't pierce anything. That's him looking at his old rebellious self and admitting it has gone soft. The ending swings hopeful, lighting the contradictions he can't understand on fire until they turn into きらめく星のかけら (glittering fragments of stars).