And I agree with the earlier posters - age is a big factor here, and not just because of the additional self-discipline and knowledge that it tends to produce. Assuming that you're starting something in a field you already know well, you probably have a lot of people you can call on for advice, help, resources, etc., not to mention more than a few credits in the favor bank. In other words, you're really not as solo as you were in your early 20's. Nor are you as likely to spend as much time trying to define your market, identify your customers, and work out your acquisition costs.
In other words, your need to iterate is probably a lot lower, since and older founder is more likely to be operating with a measure of specialized or otherwise hard-to-get insight, and are aiming for something specific that isn't low-hanging fruit, and that may depend - critically - on well established relationships.
From what I understand, the tech world is one of the few places where founders are commonly so young. I've lost the citation, but I believe the average age for start-up founders in the broader economy is 38.