Interesting. I don't know that I've felt imposter syndrome since my first year or two as a programmer. If this persists for a long time in to your career, yet you've received pay raises, promotions and positive feedback from your manager/colleagues, perhaps it is time to start questioning your belief that you don't belong. While I'm not sure if imposter syndrome is common, almost everyone holds beliefs about themselves that are either not true or that while true, are not useful and could be reframed in a way to be more useful. Most people don't question these beliefs, but we could all do ourselves a favor if we regularly questioned our self judgements a bit more.