I agree investing this 21 BTC to some business venture that will enable us to gain profit or multiply our holdings. It might be a bit hard but, everything that gives a great result is hard in the beginning then when you mastered all this all arounds of your business, it would be easy for you since you are now familiar to everything.
Somehow investing that some amount of bitcoins is going to be a good choice but I guess I will not going to invest all of it. I am going to remain some of it maybe only 5 bitcoin is going to be used for investment. And the rest is going to be stocked to my bitcoin wallet and going to wait for the price increase and once the price increased then I will sell it.
then don't wait and start doing something with that kind of money instead of leaving it idle in your wallet to stay there for a maybe!
you can start a business and earn more money with you current money and add to your stash instead of waiting.