I'm a 64 year old male with mod severe cervical spond. what is the probability of it developing to spondylotic myelopathy? i stretch, massages.

Depends: Cervical spondylosis is degeneration ("arthritis") of the neck portion of the spine. If the degeneration narrows the space for the spinal cord, you may develop myelopathy. If the canal remains adequate, you will not. It depends on how large the channel (canal) is to start with. Stretching and massage do not affect this.

Maybe: Sometimes, these severe cases result in an auto fusion and do not really progress any further. If the size of your spinal canal is not compromised, then you would have to live many more years for any further progression and potential compromise as it took you 64 years to get this far!