The more interesting trend, as you mention, is what this is doing to the career opportunities of the next generation. Since boomers aren't retiring, the top jobs in many organizations aren't opening up. And so many people my age and slightly older (I'm a very early Millenial) believe there's no possibility for advancement on the corporate ladder. Hence the recent trend towards entrepreneurship among young Gen-Xers and Millenials.

Whether this results in a net inflow or outflow in the capital markets depends on the real economic growth of all these startups. If they really do open new markets, then the economy expands, more money flows into savings, and the stock market keeps going up. If they don't, then the non-retirement of boomers just means a transfer of savings rates from the young to the old. Boomers won't have trouble supporting themselves in old age, but they'll have to support their kids.