@Mia-Clarke I don't have a lot of experience with this, but I'll share what little I do have and hope it helps. I do have an agent, who I've been with for about 8 months. She has yet to bring me work, but that said she is a new agent who is just getting started, and I am as yet unpublished. She has a fairly small group of illustrators that she represents, and I know that most of them have had work come in from her. I think sometimes it can take a while to get the ball rolling. I agree with everyone else though that years sounds ridiculous. I think I would be looking for a new agent long before that!
That said, this is the value I do find in my current agent. She comes from the editing world, and so is a wonderful editor. She's willing to look at anything I write and help me polish it up, so I'm working on a couple children's book manuscripts with her. I know some agents don't like you to look for work on your own, but she told me up front that she doesn't mind that, and that when clients approach me because I've contacted them, I can either handle it on my own, or involve her to help with negotiations and contract. For me personally, I appreciate this flexibility.
That's wonderful that you got 4 offers at once! I feel like as you interview the other agents it will probably become clear who is the best fit for you. And it wouldn't hurt to ask the others about how much and how soon you can expect work! Their responses should help answer your question too. Good luck and congratulations on having so much interest in your work! Thats a great sign.