Many pet shop clerks know very little about rabbit care and they may often give wrong information. As sarahthegemini said, greens are usually introduced around 12 weeks of age. A young rabbit, like yours, does need the fats, vitamins and nutrients from pellets. At around 6 months of age, you can decrease the pellets and only feed a small amount, according to the rabbit’s weight. A medium size rabbit (5 – 7 pounds) would get about 1/4 cup of pellets a day. Larger or smaller rabbits could have more or less, according to their weight. Some people feed less than the suggested amount, only giving their rabbits a spoonful a day. Rabbits should have access to hay at all times. Grass hays, such as timothy, orchard, oat, are best for adult rabbits (over 6 months old).
If an adult rabbit is on a pelletless diet, they are supposed to have a variety of around 15 different veggies/greens a day in order to get the nutrition they need. They would be pretty hard to manage, plus would be rather costly.
When you do start on greens, start with one, then a few days or a week later, you can add a second one, and so on.
Here are 2 good articles about veggies and fruits:
http://rabbit.org/suggested-vegetables-and-fruits-for-a-rabbit-diet/
https://binkybunny.com/BUNNYINFO/VeggieList/tabid/144/Default.aspx