Fresh Start will reset you completely.
You do not have the option to Prestige becuase you are a Prestige Master - assuming this is legit, or no?
Thanks for posting in our forums! As with any prestige reward option, you must have a prestige token to use this feature. The last one that is rewarded should have been from going from 9th prestige 55 to 10th Prestige 1. If you had used the last token, or no longer have any more, you will be unable to use the Fresh Start reward. ^JG