Your muscle length is the length between where the tendons at each end of your muscle attach to your skeletal structure.1 Your muscles will never be wider/bigger than they are long, so your natural length plays a part in determining how big your muscles can become through training.
On thing to keep in mind is that the length of your muscles varies throughout your body. While you might have long muscles in your biceps that you can show off easily, you may not be able to get that level of definition as easily in other muscles. And it's very rare for someone to have all short or all long muscles.3
As far as your skeleton, assuming that you are well nourished and relatively healthy, you skeleton will not change a whole lot. Especially in bodybuilding, where the ideal is broad shoulders and narrow hips (with about medium length arms), those perfect ratios are something that you have to be born with.
Most importantly, though, realize that your own drive will, ultimately, be the main thing determining your level of success. You may not have the genetics of an Olympian, but through diligent hard work (and tons of enthusiasm!) you can make bigger changes than you imagine.
Your unique bodybuilding genetics are neither a blessing nor a curse. They're just life.
