I agree with atonicat. Bone spurs are growths of the vertebrae that are a part of the wear/tear of the spine that goes along with ageing. It's as common, and generally goes with deegenerative disk disease. Think of it as an extension of the spinal disks or bones. And yes, they can causde pain, in your case lower back pain.
Bone spurs are just extra bone. They become painful if they rub against another bone, and could lead to arthritis. The fact joints are what allows the spine to bend. So the spurs can cause stiffness and impair you ability to bend your spine to a certain extent.