I`ve seen this graphic posted on some other forum thread before.
There`s plenty of space for bitcoin to grow,but it`s wrong to compare it to gold.
Gold is used by the people for centuries.All the people without computer knowledge will trust gold,and believe me,most of the people in the world don`t have a PC,which means that they don`t know anyhting about btc and most likely they will never buy and use bitcoin.
The most important aspect is not the amount of people using bitcoin but the amount of money invested in the bitcoin ecosystem, if someone does not have the resources to access a PC then that person will probably not use bitcoin anyway, it is the middle class the ones we should aim for since they are the ones that are spending their money and have access to all the necessary tools to use bitcoin already.