As long as they can understand the concept of riding, they can ride a bike.Actually, many mentally handicapped people are highly intelligent
in their own way.
My brother participates in the Special Olympics. Cycling IS an event of the Special Olympics. So differently abled persons not only ride, but compete on bicycles!
The level of retardation that would make it impossible would be one that effects their motor functions as well as their mental faculties.
People with disabilities can ride bicycles. one in four amaricans can be diagnosed with a disability. second part all depends on what kind of a bike they have.