I suggest to play all your games on beginner. I started in the Light Heavyweight class and after 9 wins I got a shot at the belt. I won the fight and defended the title 5 times. Then I got the option to change weight class. I went for Heavyweight and I received the achievement "A Change of Pace". After that I just kept winning and after you reach 1 million fans your longevity will be extended.
At the beginning you may think you can't reach 30 fights but your longevity will extend when you get more fans. So just keep playing and eventually you will have 30 fights. But like I said at the start, playing on beginner is adviced. You win games quicker and easier and if you win everything you will gain more fans which will extend your longevity.