If it is a consumer product targeted at young people, then no experience is necessary. Would a young Zuckerberg get enough experience to start a social network after a stint at Yahoo or Microsoft? Probably not. His product relied a lot more on the understanding of the young, college-going audience. The concept of social networking was new and existing experience really didn't matter as much. Thus, many consumer-centric companies are founded by younger people with lower experience.
However, an enterprise product is a totally different game. It is very hard to understand the market and prior experience and connections do matter. The startup I'm working for has gone past the Series D stage and among the most successful startups in Boston. It deals with software risk and logistics. It would have been very hard to cofound this one by someone just out of school. Apart from Box and Dropbox [which both started from consumer segment, there are very few examples of successful B2b entrepreneurs without experience.
Some products where experience mattered:
Reid Hoffman worked a decade before he founded LinkedIn. It targeted more senior workers and execs. He and his cofounders spammed their entire network to get the initial signups.
Arrington had a decade of legal practice experience before founding TechCrunch. He depended on those initial connections.
Mongo DB's CEO Kevin Ryan has decades of experience and so is Zendesk founder Mikkel Svane.