Is the life expectancy for someone with scoliosis shortened?

No: Unless the scoliosis deformity is significantly large to cause the diaphragm to not be able to work correctly causing diminshed lung volumes and pneumonia. That would be very unusual- most people intervene early enough to prevent any situation like this.

Only severe cases: Scoliosis does not typically affect life expectancy. The one exception is when the spinal curvature is in the thoracic spine and is serve enough to compromise lung function. This requires surgery to straighten and stabilize the spine.