Add a time limit. You got 1-2 months optional amateur fights after creation. if you didn't take any amateur fights during that time period you are no longer an amateur and automatically become pro. Once you turn pro no going back.
Amateur fights should also be booked faster instead of a 2 day waiting period it's a it's 1 day QFC.
Would have to also be no hype gain otherwise there would be little incentive to go pro. No energy loss/hype gain when amateur, turn pro and can gain hype but all fights burn energy no going back.