This is a polite way of saying "How long will you work for us". This is a company that wants to keep you FOREVER. They want you to work for 40+ years. You should answer with something like I would like to stay with the company and move on to be something like a project manager. Basically anything that indicates you want to stay with the job. I don't see why you wouldn't want to though, it's a great place and you get amazing pay.