How long is normal to be assigned with a client?

I’ve been working with one of my clients for almost a year now. I work in home for a company that does not have a clinic within my state, so I have been this client’s only RBT. I love working with him, but I’m worried that he’s not making much progress anymore and that we’re stuck at one level. He’s mainly learning life skills, which he has the ability to do but he needs the extra motivation. How long do most RBT’s work with their client for? I don’t want to leave the case but I’m worried that we’re not making as much progress with him as we could be.