You only need to keep entire males separate from females (their mums and aunties as well as their sisters
) from when the boys become sexually active. In general we say that’s around 4 months for most breeds - but I ring my boys, so if that’s too long, hopefully someone who keeps males entire will jump in!
As to ‘how old to slaughter’, it’s not about age it’s about condition. This will vary greatly according to breed and local conditions, but will also vary between lambs of the same breeding brought up together. It’s also important to know your market - if you’re sending lambs to a primestock market, the ideal lamb weighs around 42-45kgs on your farm (and will weigh 2-4kgs less entering the ring, after the journey and waiting on cement for a few hours) and has a condition score of 2.5 to 3.5. If slaughtering for yourself, you can keep them to quite a bit bigger and get more meat off them. For a butcher or a box scheme, somewhere in between the two.
What ewes do you have, what tup did you use, who is the meat for?