Entrepreneur: the word may conjure up images of passionate, driven young people -- perhaps still in college -- with limitless ideas and not much to lose. With 30-under-30 lists abundant in business publications around the country, young entrepreneurs are lauded because they are indeed exceptional.

They are exceptional in part because they fall outside the norm in terms of the average age of a successful entrepreneur. The "I built this company in my dorm room" story makes for great reading, but in the meantime, most successful entrepreneurs have at least a decade's worth of experience on these young guns. According to a recent study from Harvard Business Review, the average age of the successful startup entrepreneur is 45.

The study points out that many consumer-facing startups in spaces like social media have public-facing young founders, while startups in business-to-business categories like oil/gas and biotech tend to have founders with more experience. This creates a gap in the public perception of what an "entrepreneur" (in the press, at least) looks like.

The more experienced founders had higher success rates, whether measured by sales growth or employment growth. Quoting HBR, "Our evidence points to entrepreneurial performance rising sharply with age before cresting in the late 50s. If you were faced with two entrepreneurs and knew nothing about them besides their age, you would do better, on average, betting on the older one."

Which traits of successful entrepreneurs get better with age? Here's the shortlist:

Leadership -- You can read or write about leadership all day, but until you spend some time in the trenches dealing with a crisis -- a turnaround, a failure, or any number of other leadership challenges -- you're not as ready as the person who has. Every leader makes some mistakes along the way and learns important lessons on that journey.

Self-Awareness -- This dovetails a bit with leadership, but age and experience certainly bring a stronger sense of self and understanding of our own personal strengths and limitations. This knowledge is critical in terms of understanding and accepting where and when to bring in partners who offset what you do and don't do well.

Reasoning -- The more negotiations you've worked through, problems you've solved, strategies you've executed, and planning you've set forth, the stronger your reasoning skills are. You've seen the pitfalls related to these areas and know what to look for to set yourself up for success. Reasoning can separate the dreamers from the doers when it comes to charting a course forward through a challenge. Experience has a strong upper hand on this one.

Grit -- Or call it perseverance, or resolve, or toughness. An entrepreneur who has weathered a few storms will generally hold up better in trying times than a young entrepreneur with loads of passion but no experience.

Passion -- This word is typically associated with young founders, but experienced entrepreneurs have a high level of passion that often comes from witnessing a hole in a market they are already entrenched in, and making it an opportunity that may be more quickly funded and realized. On top of that, many of these entrepreneurs have learned both what to do and what not do from their former employers -- and they are committed to putting that in the new business.

Stories of young, successful entrepreneurs make headlines because those leaders fall outside the norm of the business world, but that doesn't mean that 25 is the deadline for entrepreneurial success. If you are in your 30s or 40s and looking to start your own venture, you have a pile of advantages in your corner, including a track record of performance and returns. Know that 45 is the new 25, and charge forward.