I started giving Blueberry veg from about 10 weeks.
I started with a small amount of carrot for a few days, then a small amount of spring greens again for afew days just to make sure she was ok with them.
I kept introducing veg like that, then gradually have increased the amount.
I still adding new foods now in small amounts for afew days along with larger amounts of what I know she's ok with.
There is a big list of food's in rabbit edibles thread that are safe to feed.