Hmm I feel like most founders I know just started companies after college without much experience. While people that want to get experience first seem to never end up starting a company. I think it mostly comes down to risk adversity.
I am absolutely not saying you can't do this. In fact, GoCardless is an example of a company started by very young founders with little start-up experience, and is now a unicorn.
The difference is that if you have this experience when starting a company, it can help you avoid so many stumbling blocks, and you can skip forward to more mature company stages.
While you can't really compare two companies, I think it's interesting that the company I currently work at (incident.io) has only taken a year to go from me joining as the first employee to 40 people + series A + hundreds of customers now.
There's no way we'd have moved so fast if it wasn't a case of replicating what we already knew worked, tweaked for the environment we found ourselves in.
So yes, it doesn't mean you can't be successful as an inexperienced founder, but I do think it makes a difference in terms of execution.
I think this may just be your bubble - I'm 39 and worked as a programmer since I was 18 in 3 different cities/countries & I know lots of both experienced people and people out of college who started companies.
Is a "startup" the same as starting a company? If I start a company without ever seeking external funding/accelerating/etc, is my company a "startup" in the same way that "founding a startup" implies?
I was under the impression that starting a company in general and 'starting a startup' are not exactly the same thing, though I surely might be wrong about this.
I think the average US founder age is 40s. But I'm not sure since most statistics focus on successful founders. This link seems to look at all of them.
The average founder of a business is not founding a VC-targeted startup, or even a technology business. There are a lot more landscapers counted in all of these surveys of successful startup businesses than founders who even considered YC.