Just copied this from Defra-
(4) Under the Protection of Animals Acts 1911 to 1988 (in Scotland, the Protection of Animals (Scotland) Act 1912 to 1988), it is an offence to castrate a goat, which has reached the age of 2 months without the use of an anaesthetic. Furthermore the use of a rubber ring or other device to restrict the flow of blood to the scrotum is only permitted without an anaesthetic if the device is applied during the first week of life. Under the Veterinary Surgeons Act 1966, as amended, only a veterinary surgeon or veterinary practitioner may castrate a goat after it has reached the age of 2 months, or dehorn or disbud a goat, except the trimming of the insensitive tip of an ingrowing horn which, if left untreated, could cause pain or distress.
So yeah surgery any age as long as anesthetic is used after they are 8 weeks.
What age do people have them done surgically? I see that ringing must be done within first 7 days.