Thanks for your question.
Although the testicles of these guys are present in the scrotum at birth, castration is not recommended until they are at least 2 weeks old, by which time the elastic banding method is not appropriate.
It is therefore more appropriate to castrate using local anaethetic into the scrotum after 2 weeks of age. Once the animals are over 12 months old they may require sedation to be done standing or anaesthesia to allow them to be done on their side as they may be too difficult to steady if done with local only.
I hope this helps,