To be a Gladiator, your level must be over 40 and you need to collect the Mark of the Challenger, the Mark of Trust, and the Mark of the Duelist.
Your level is still insufficient and you don't have the 3 marks. Come back to me after more training. Come back after you have collected all 3 marks and increased your level to 40. Then I shall change your occupation to a Gladiator.