What causes low back pain on both sides of back?

Several Reasons. The most common in your age group is multi-level degenerative disease or arthritis of the spine.
Spine Pain Options. This chronic pain in the distribution as you suggested is the result of an irritated nerve or facet joints or other injury typically in the lumbar spine (low back) which are caused by herniated disks, spinal stenosis or degenerative disc disease, etc requiring further evaluation by a spine specialist and may be candidate for facet injections/radiofrequency ablation and epidural steroid injection.