Bitcoin IS investment already! 
You may think like that, but there are more investments with Bitcoins. We can trade them in websites and with some experience you can make a good profit.
Gold may be able to compete bitcoin on the future since gold also have a chance for made profit because gold's value keep increase overtime
In other side, bitcoin still consider as risky investment so don't invest on what you can't afford to loss
There is no guarantee that the price of gold will be only higher in future and it may also go down as we cannot be sure about any investment that it will give only positive results and bitcoin is good to make short term profits.