Now there's a thoughtful article by Diane Mulcahy, a senior fellow at the Ewing Marion Kauffman Foundation and an adjunct lecturer in entrepreneurship at Babson College, on the topic called "The New Reality of the 14-Year Venture Capital Fund." This Institutional Investor article discusses recent data that indicates that the median fund takes over 14 years to end. It's a very interesting article and worth a read.
In my experience, the strategy of the fund and vintage can influence the overall lifespan of a fund. So for example, 1999-vintage funds that invested in early-stage technology companies had two economic downturns to work through, which extended the lives of these funds. Conversely, later-stage funds that invested in pre-IPO tech companies in 2006-2007 will likely have shorter lives. I have worked with several funds where the life span was well over 14 years, so this article was very interesting to me.