Beautiful Child

It means that at the age of his love with someone in his life, say at 18 or whenever, at that time in her life (somewhere across the world) she was at the age of only 10. They didn't know each other at the time, she is just pointing out the age difference of experiences that was happening at that time. Like when my husband tells me he saw David Bowie back whenever, I say to him "Wow, and to think I was in kindergarten then!" He just loves that.