This is correct. Many sources say exact same thing, but they also mention one fact, which you missed.
They all say you should start with this in your early 20's. That's the most fruitful time to do it, so you can enter your 40's with a nice passive income
at the age of 20 years, humans do not have many necessities of life, so they are free to work as they think. that way they will have various experiences and overcome the problems they get, so that with increasing age their psychologically matures and finally they will have financial freedom at their relatively young age.
because at that age humans want to feel freedom and want to do many memorable things in their lives. but at this age a person should have started to think about his future, start planning what to do after graduating from college and start looking for business opportunities. 20 years is a crucial age for a person because at that age he begins to form his identity.