Welcome to Just Answers, I will do my best to Answer your Question.
First of all, congratulations on meeting your goal.
Secondly I'm going to respond in it's proper perspective as to when a "Hobby" becomes a "Business"
When you decided to choose professional golf as your career then it's not a hobby, the training, the fees, and all the expenses now become a personal Schedule C deduction from your taxes in which you can go back three years.
You can take the losses for three to five years
You can choose to LLC or S Corp at any time or any type of Corp. as you wish which I would defer you to a Corp. Tax Attorney that can set you up properly.
You can expense your expenses in obtaining a sponsors
So, if you need to amend your taxes to go back three years, you can, the law allows you to do so.
Your desire, and your choice to become pro is what determines your position as a pro and the training it takes to get there.
Thx for the info. Just to clarify - I could recapture my expenses for only last three years but in order to do so must go back and amend last three years of taxes. I am also limited to losses for three to five years?