My son is 14 and was diagnosed with sbo during a CT scan for spondylolisthesis at L5 is there an operation to close the defect in the vertabra?

Spondi. Most often, surgery is not required to treat this. If your son does not have any pain in the back or legs, then surgery would not be recommended. This is often a developmental issue where the bone does not completely ossify (form) . Your son is most likely still growing and developing his skeleton. You should see a spine specialist, perhaps a pediatric orthopedic doctor that does spine.
Depends on situation. This disorder is caused when a vertebrae slips forward on the one below, usually L5 over s1. It veries in degree of slippage. Those that are most symptomatic can undergo a posterior fusion using grafts.