What to do in your 20s, 30s, 40s and 50s to retire with enough money

No one will ever save enough money to retire. Consider instead building a source of income that doesn't require daily personal effort. Income-producing property. Income-producing investments. Building a successful small business that can be sold for cash plus profit sharing. Etc. Etc. Etc.

I know young folks don't want to hear this but don't use Debit or credit cards, use cash. If you do use a credit card pay it in full at the end of each month. It is amazing how quickly credit card debt adds up if you don't pay it off at the months end.
Understand the terms of any loans you take out for education. Yes, it is your responsibility to pay the loan back; not the taxpayers or the lender you took the loan from.
Basically, don't out spend you income when you are young.