I just purchased an 11 month old filly and an working with her right now as well as a 3 month old foal. Mentally the yearling is about the same as the foal. I have been working on building her trust in the pasture, walking up to her with a rope, fooling around with touching her back and legs, backing off and repeat. I am trying to make them both easily caught horses even on a large pasture.
We are also working on space respect. On the lead I work with them on keeping their attention for short bursts of time, having them move their back ends away, backing up to pressure and cues, being soft in giving their head, being used to being touched around their ears and teeth, etc. basic things that would be much harder at 1000 pounds.
Keep posting your progress and maybe some pics?
Riding: The art of keeping a horse between you and the ground.