I do it (with Black Welsh Mountain sheep), they need to be 60% of their mature weight though. And you need to ensure that they have adequate food over winter as they will need to keep growing themselves. Don't overfeed pre-lambing though, you don't want big lambs.
I find them brilliant mothers, and I find gimmers lambing for the first time to be a pain in the ass!
I lamb outside though, i don't know what they would be like indoors. One thing I would add though is that I tend to bring mine in once they have lambed, just for 24-48 hours, and I've noticed that sometimes it can be tricky getting a ewe-lamb to come in by following her lamb(s), especially if the rest of the flock is around, as she hasn't yet learnt that she needs to stick with her lambs rather than the rest of the flock. To get around this, I leave them outside for a bit longer than I would the older ones, so that they can bond, and stay well away from them if possible so that they don't move away from the lambs.
Also, it would be wise to shear the wool away from the front of the back leg/belly to make access to the teats easier, and ewe-lambs will be more wooly than ewes. Do this well before lambing time - I would do it when I do the pre-lambing vaccination.
And like TimW says, wean early.
There is a good document by the ADAS, I will try to dig out a link...
...I couldn't find the original one, I think it was called ewe-lamb blueprint, but here is another similiar:
http://www.eblex.org.uk/wp/wp-content/uploads/2013/05/breeding_ewe_lambs150512.pdf