When I was a boy and teenager, I was called "Robert". In university, I decided that I wasn't so much a "Robert" as I was a "Rob", so I went about losing the 'ert'. Even though it's been over half my life since the shortening of name (even though in my mind I'm just barely out of university), many of those who knew me before the change still call me "Robert".
So, if you're ever with me, and somebody calls me by name, you'll have a pretty good idea of how long I've known them. You know, if the police ask you.