I have spent my early and mid 20s working on copycat Startups. Some made money, some not. I have learnt entrepreneurship in the hard way like lack of funding, unreliable partners, rough market conditions and disruption by other solutions. It made me more mature and conscious in life, however I know I missed out many things my peers experienced: travels, relationships, marriage, kids, whatever makes a person happy.

Entrepreneurship can be extremely hard. Believe me. All the people who become successful in their 20s by starting a company is just a small fraction of whoever tried.

However entrepreneurial mindset is very applicable for most of the jobs and useful mindset in every aspect of ones life. Trial/error/retry, build-measure-learn like Lean, any Agile framework teaches the same: adapt to change. It doesn't matter if you are about to build an app or try out a new sport, you should always be open to adjust your strategy to approach things.

Don't be afraid of spending your 20's/30's in employment, whichever company, your brightest ideas will come later as you progress in life and career. You can still surround yourself with people who are wiser and more experienced regardless of your current occupation.