凉薄少年已无心
[liáng bó shăo nián yĭ wú xīn]
This implies a young person with a disinterested or emotionally detached attitude ('heartless' in a sense). It suggests that through various experiences or over time, the 'cool and shallow boy' has now become emotionless or unenthusiastic towards certain things in his life, maybe after heartbreak or other disappointments have dulled his initial youthful exuberance and fervor.