Perhaps mroe than 50%? Or maybe not because not much country even developed country uses it
in 2020 if 20% of the world start using bitcoin i think it will be a good progress, as still there are so many backward countries who educational ration is still very low, their people have very little access to computer and internet. but we can expect that the new generation will be more educated so we can expect that they will have access to interment and computer in future but still it will take more than decades when these people will get benefit from bitcoin.
That is totally unrealistic, because right now bitcoin is almost 7 to 8 years old and still we have just 1% or maybe near 2% of worlds population using bitcoin and i don't think that we will grow to 20% or higher in just 5 years, even if we touch near 10% around 2030 then that would be great because the population of world is really enormous.