An executive creative director once told me that one of the most important things she could do as a manager was to make sure she understood what each person in her department's personal goals were, then try to give them a path to those goals.
Because there's a lot of upward pressure in our industry (or maybe it just has more to do with the American psyche) the perception is often that there is one path:
JR CW/AD >> CW/AD >> ACD >> CD >> GCD >> ECD >> CCO >> PRESIDENT >> JR DEITY >> DEITY
The truth, however, is that a CD job isn't a good fit for everyone, either because of skills or choice. A lot of creatives would prefer to stick to what they love--actually creating the ads--and avoid the meetings, politics and other B.S. that come with a management position. There's nothing wrong with this. Your boss won't see it as lack of ambition (or at least shouldn't).
The key for you is to figure out what your goals are and to let your boss know about them. Sometimes there are official channels for this, like annual evaluations. If not, find a good time to have a meeting. Let them know what your goals are and ask them what you need to do to get there. What do you need to work on and improve? And if it's not your goal to be promoted to the next level, cool. You just need to know where you want to be in a few years, because if your boss asks you, the worst answer you can give is "I don't know."