It seems he might have mechanical back pain ,he must go to a orthopedic doctor for referral, after xray or mri if the diagnosis may be either lumber spondalytis, mild disc prolaps or spondylolysthesis etc then he may go for the conventional medical treatment with physiotherapy management ..
Next Steps
I hope with few sittings of physiotherapy he may recover ..
Health Tips
spinal execises & core muscle exercises..