Here's a fun little retirement calculator everyone should play with.
http://www.mycalculators.com/ca/retcalc1m.html
According to Wikipedia, The Donald claims he was worth $200k when he finished college. I'll go ahead and assume he's lying about that because everybody lies about how great they are - everybody in ATOT makes at least 7 figures and drives a Ferrari. Let's round Donald's number up by a factor of 10 and assume he started with $2M. He's about 70 right now, and we'll assume he started his retirement career when he was 20, so that gives us 50 years to create $4B. I'll assume he always lived like a playboy since he was born into a rich family. Average income back then was around $3,000, so we'll give him 20x that much to maintain his awesome lifestyle: $60,000/yr in 1966. Now fill in these numbers:
How many years until you retire? 0
Number of Years in Retirement: 50
Average Annual
Interest Growth Rate you can earn? Enter the number you think is required.
Compounded: Annually
Average Annual Inflation Rate: 3%
How much $ will you have when you retire? $2,000,000 (what he started with)
Do you want to have any money left? $4,000,000,000 (number he has now)
Adjust for inflation? yes.
After trying different numbers, the required rate of return I'm coming up with is 20.5% annually to be able to maintain that playboy lifestyle (~60k/yr) and grow your net worth at the same time. That needs to be maintained every single year for 50 years in a row. That's pretty good. That's in the same league as Warren Buffett and Carl Icahn.