When a child has tight heel cords & toe walks, how old is "too old" for serial casting to be effectv?

Usually < 2years old. Tight heel cords can cause toe walking. However, a condition called tethered cord, where the spinal cord is attached to the base of the spine and stretches the spinal cord can result in later toe walking and decreased reflexes in older child. Mri to rule out tethered cord is important before serial casting or other treatment is undertaken. Tethered cord requires neurosurgery to the cord.
Depends. A thorough evaluation is needed to determine why a child may be toe walking before consideration of treatment options. This includes the timeframe that the child has been walking like this, milestones, life stressors and congenital and neurological disorders that may be present. Conservative care includes physical therapy, serial casting and monitoring. If this fails, surgery may be indicated.