This is a very interesting post, and one in which I can relate.
The quick answer is an average young person with absolute dedication towards their goals can in fact create a fortune of $100MM or more in the span of the time frame referenced.
How do I know? I've seen it first hand, and was on my way (well, pushing 10% of it). Of course that's before the doctor severed my capital limbs (the doctor being the not so great recession).
I was raised in an atypical blue collar family and community in So Cal. Always being entrepreneurial minded I left a management job in City Government to go to work as a commercial real estate agent at 27 y/o. By the time I was 35 I had bought several large commercial buildings, and embarked on starting a commercial development company.
My net worth was substantial, and cash flow allowed for a very comfortable lifestyle. By then I had moved my family to Newport Beach, CA where many of So Cal's large real estate companies and investors reside. My wife and I entrenched ourselves in the community and I got to know many, many of these real estate folks through involvement in our kids private schools, their community sports activities, and the non profit boards I sat on.
I heard how individuals on their own, brothers and sisters, cousins, families, and friends pooled together resources to start buying real estate. And those purchases continued over many years. Some of the real estate owners were benefactors of previous generations, but the vast majority were self made. In fact, my development company partner and I met on one of those same sports fields were I met many other real estate folks.
The development company didn't work out, but to give you a perspective of how you can get to the type of net worth that's the subject of this thread we had five projects across the state of California from San Diego to Palo Alto and each was at a minimum 18 acres. We had planned on building small business parks, and had the land in escrow or under contract. We even had Toshiba lined up for a 15 year build to suite lease, but it did't work out. We were to capital constrained, and when we needed capital the most the hedge fund Long Term Capital imploded and brought lending to its knees in commercial real estate for some two years.
But had we executed just a year earlier we would have probably gotten all of our deals funded. And the exit would have gotten my family closer to the subject net wroth as opposed to further away from it.
There have been many comments here that have mentioned luck. I don't believe that to be true. I instead believe that the harder I work, the more detailed I am in my processes, the more people I meet, and the more respect I extend to others the luckier I will become.
Build a plan, put your head down to execute, and then go do what needs to be done to get you to your goals. Happiness isn't delivered through the wealth, happiness is found in the process.