Does an old buckle fracture show up in an xray? serious excruciating pain. please help

Yes it does, a ---: - buckle is seen in the cortex of the bone, hence the name. Usually in youth,in younger years. They may be very subtle though. If suspected a cast 2 protect it & films in 2 weeks, and then there will be evidence of healing callous present. @ 40 years it's unlikely, you would be more sustable to have a stress fracture. These develop slowly, so if this is an acute injury see an orthopedic surgeon.