Yeah, most women that are career-oriented tend to be T-driven women, opposed to E-driven but, make no mistake, women are women are women are women and what a woman wants remains the same: a strong and confident man. So, if you're getting dates with these women then that doesn't seem to be an issue and I'd say "Are you a manager?" question is just gauging you to see how you react, your position and title are pretty irrelevant.
What happens is a lot of guys here that question and think "Man, she wants a guy who makes a lot of money, etc." and they get nervous and start to lose sight of what a woman really wants and then bend/twist themselves to fit the mold that they think she's looking for and lose her because of that. A woman wants a man that makes her feel like a woman.
Anyhow, to the actual question itself:
"I'm actually the janitor" is something that I would use because it shows that you're not fazed by her question provided she's trying to test you to see if you get fazed or not. If she's testing you for particular traits or qualities that a "manager" has then you respond with something different, like, if she's saying "Are you a manager?" to really ask you "Are you a strong and confident guy who can lead people, handle the stress of the workplace, etc.?" then I'd probably go with something like "Being a developer suits me much better, I find that building and writing software/applications is where I shine, it's like problem-solving in real time, tons of stress to debug and troubleshoot potential problems and then it's a puzzle to figure out the solution. Being a manager wouldn't quite do that for me."
-Richard