We don't know the time when does bitcoins could last. As bitcoin price continue to increase, many people will attract and push them to start earning bitcoin. And maybe after 20 to 30 years, there will a lack of bitcoins but it is just my opinion.
Ofcourse no one can predict the age of bitcoin,but the value of the bitcoin is constantly increasing these times as well as sometimes the value of bitcoin falls little bit.when we research about the bitcoin statistics,it is doing much more better.As you mentioned there maybe lack of bitcoins in the future .so be wise and act immediately investment on the bitcoin will surely gonna be a better Investment in the future.
I agree that bitcoin cannot be predicted as long those people who using it are doing into the right way. The best way to help people by there financial problem.
But I'm hoping that bitcoin will last many years so that, many peole not only me, us, and every body will be solve those no work and to lessen unemployed peoples.