If you really look in detail at the history of practically any composer, you will find that none of them were ever born that way -- they were created or developed. The myth that great musicians were born talented arose because people couldn't believe that such insurmountable differences in human capabilities could be developed. But that myth is based mainly on ignorance of the real facts.
Logically, it is not difficult to convince yourself that being born with music is impossible, mainly because music is a totally human concoction. Otherwise, why wouldn't an Afircal pigmy start composing Beethoven sonatas if he happened to inherit the right genes? You might laugh and say that's utterly impossible -- but think about it -- that means you knew it all along!
Music is like religion -- it is a totally human creation. So if you can create God, (Jesus, Buddha, etc.), why not a mere mortal musician? All you need is love, desire, and enjoyment of music -- and a little research wouldn't hurt either. Welcome to reality!
How do you get there? If you have no idea yourself (a bad sign -- it will probably take you a while), then start making music by practicing. As you start playing different composers and different genres, you will pick up plenty of ideas. Theory is not necessary and, some say, can be detrimental at first.