How far back (in years) can I go to claim expenses I used in starting my business?

Background.... It is a photography business, a portrait studio in my home. While I was working a full time job and a part time job. So the road has been long. Then, I know the IRS their going to say, hey, that's just a hobby. But I have documentation where early on, I was intent on designing and developing a website for it for business purposes. I also have files and education on it being a business. I have the sole intent of doing it as a business and not a hobby from the get go. So that my question comes back is how far back can I go to capture the previous year(s) expenses? I did some research and I see nothing on it. (hard number in terms of years and a cut of point) But, i do see only intent of action! (I was not a hobbyist of saying, hey, I should try and make money out of this.) It was my intent for the very beginning from day one! So, if someone experienced in this area would be great!! Thanks.