We usually send them off in August at 16 months, but with Soays we sometimes keep them for an extra year so they go at 28 months. It is of course better to castrate them, but it can be very difficult to do it properly within the stated 7 days of birth so you could end up with a rigg anyway. There is more meat on a mature Soay than you might imagine and it's very tasty - very different to baby commercial lamb, different to Shetland, different even to Hebridean. People talk of 'gamey' but to me that is a negative description, but Soay meat is close grained, darker than young lamb and almost fat free.
The question of tup taint is often discussed but I think in the end it's a personal thing - some people are sensitive to it and some are not. Try sending off the ones you have next August and see what you think of them on the table. If they do have any taint then they make great curry, which disguises it. If your butcher is not used to cutting Soays he may want to discuss with you just how you want it done. Chops will be tiny, even valentine chops, so you may prefer rib roasts or some other way of dealing with that bit. Gigot and shoulder are a reasonable size though.
We 'visit' the carcases once the butcher has them hanging. This gives us an idea of how well finished they are, we can help the butcher to decide just how to go about cutting them, and we learn plenty from the butcher about meat and about how to grow our sheep.