I would not band him at that age. Take him to a vet and have him castrated. I don't know what breed he is but most goats are very well endowed at that age and banding him would be cruel plus could cause more problems.

I would not hesitate to band a 5 month old. Actually, the longer you wait the better the uretha develops to help prevent UC later in life. If the band is placed properly, or 2 bands if needed, then the chances are slim for problems. The area becomes numb quickly. Be sure to Booster his CD/T.

If the buckling were 9 months or older, an adult buck I would not band him myself, for several reasons not just those stated above.