If the price doubles every year, the price could be $6000 in 2020. With 100 bitcoin, you will be worth $0.6 million.
Doubling every year is hoping too much.
Somebody offering those returns would be called a ponzi operator.
The price will not double every year , the doubling of price of bitcoin occurs only in the halving and after that a slight and regular increase will occur in the price of bitcoin with the passage of time, so with 100 BTC we can not be millionaire in quick time.