My son has been diagnosed with bilateral spondylolysis at L5. What is the best and fastest treatment?

Simply:

In most cases, complete rest is the treatment of choice. For around a period of 6 weeks, to allow the bone to heal. A back brace can be used and its always a good reinforcer in reminding the patient that they shouldn't do too much activity. As for an operation, that is not my field, however physiotherapy will help this issue.

As the bone is healing a progressive exercise program may commence, usually starting with exercises to increase the muscular stability in the lower back, however you should see a physiotherapist in the flesh, rather than advice from online clinitions such as myself as, depending upon response rate, the exercise programme can be tailored.

Although a general answer to your question, at 13, it is imperitive that your son allows this vetebral injury to repair itself. Your physio should then allow a gradual retun to sport and include further enhanced exericses to help with stability, control etc.....

Regards
Liam Robinson