It's the Roman numeral for 10. 5/5/89 is my birthday: 5 plus 5 is 10, and this is my tenth year since I got into music. 'X' is the 24th letter in the alphabet, and I will turn 24 when this album comes out. 'X' is also a metaphor, as in 'ex-girlfriend': it implies you're progressing and moving on in life, not holding on to the past and your old ways.