We don't castrate our GFD boys and we tend to keep them on until around 18 months.
The hogget meat is delicious - no sign of any taint.
I must admit we originally did try and castrate the boys but found that quite often it was very tricky to do on GFD's as the testicles hadn't descended in time.
You have an option to get the boys inspected in their first autumn or, if you prefer, when they are around a year old. The registration forms are usually sent out to DSBA members in June for return by early July.
Getting certificates has been a bit of an issue in recent years but it is getting better. Have a word with the breeder you bought them from or speak to Patrick (the secretary).