a) worked in a professional setting (e.g. a large corporation) b) managed other people c) been married d) been alive since before 1980
A person is simply the culmination of ones experiences, training and beliefs. For some, it takes 40 years to build those things and for others it takes 20 years.
Although age and maturity usually correlate directly, it's not always true. We've all met people in their 40s that act like they're 18, and 18 (ok, maybe 25) year olds that act like they're 40.
Disclaimer: I'm in my 20s
The older you get the more your perception of time changes. I think this is part of the reason that there are so few 20-something leaders of huge companies. Partly it takes time to prove yourself to enough people to get a shot. Partly because it takes a long time to be patient enough to where you can be effective at the job.
I think I'm definitely not the same person now as I was at 24, or even 29. The thing is, I wasn't the same person at 29 as I was at 24 either, and I doubt I'll be the same person at 40. In other words, the process of change and growth doesn't stop - ever. Probably that's the biggest lesson I learned in my 30s.
I think the biggest mistake many 30 and 40-somethings make is to fit everything into an overarching narrative of growth and maturation. "I was young and foolish then, now I'm older and wiser." Because the narrative doesn't actually stop - we are still young and foolish, hopefully - and trying to fit yourself to it just ensures that you remain stagnant at wherever you were at 30. Instead of a narrative of growth and experience, it's really one of adaptation, of recognizing progressively more subtle distinctions in the environment and changing yourself in response to them. And in that narrative, it makes sense to listen to everybody, even to young people, so you can pick out the parts of their experience that are new and unfamiliar to you.
Story time: My grandfather was a soft-spoken old cowboy, but you should have seen him charm and intimidate cattle buyers. At 70 years old, he could hold his own with the slick-talking young buyers because he had gone through that same negotiation 100 times and there was no trick they could pull that he hadn't seen.
Disclaimer: I'm 39.
At 15, I was living in a small village in Chile, without parents. There were 2 English speakers in this town, and we learned to work together to learn a new language, adopt a new culture, reconcile differences, and more.
Those experiences have shaped my outlook on everything from relationship management to problem solving to effective communications.
IMHO, a great way to become an effective entrepreneur is to immerse yourself in high stress, difficult situations that require on-the-fly problem solving over and over again.
Your marriage is more important to your long-term success than your start-up is, too.