Of course ordinary citizen can use the Bitcoin. The bitcoin is open for everyone to use.
They just have to know how to use. But if they know how to use is and know all the profits of using it more people will start to use it
We are all considered ordinary citizens since we are not a military personnel, government worker, politician and thus we belong to that category. Most of the bitcoin users are or were ordinary citizens of their own state and will continue to increase in number. But bitcoins is not just limited to ordinary citizens but to all citizens in the world.