Tupping ewe lambs, my thoughts:
I wouldn't put my Wilts ewe lambs to the tup, because they are slow-growing, and I imagine I might extend this principle to primitive breeds. However, fast growing commercial breeds I would, and aim to, this autumn.
My policy will be - only those ewe lambs who have attained 40KG will go to the tup, they will not be allowed to raise trips, I am as yet undecided about twins. I have heard it is a bad idea, and is likely to knock multiple births later in the ewes life. I believe that because of her age, supplementary feeding will not benefit the in utero lamb, but will cause the ewe to gain weight, possibly leading to complications, so the message is don't give them extra rations (compared to those you would normally give your ewes)
However, it is understood, I think that a ewe lamb who takes the ram in her first year will be more productive throughout her life (Ovine early oestrus somethingorother) and of course, it keeps the ewes small when fully mature which can only be a good thing - nobody wants massive ewes to feed.