Is it normal for a 14 year old male to sing as low as Johnny Cash?

Hey, I'm Quinn. I'm a 14 year old boy. And all my friends have higher voices then me. And I don't mean by like two or three half steps, I mean their voice is usually an octave higher. I can reach the bottom E on the guitar, and sometimes a little lower. I find very few songs of Johnny Cash I can't sing. But anyway, I was wondering...is this normal? And I have another question. How can I deepen my vocal range? Not higher because i can sing the G on the high E string. So my vocal range is three octaves. But how can I deepen my voice even further? I can feel it getting deeper everyday and notes getting easier, but is there any exercise to make it go deeper or what? Thanks for all your help! =�