The ball they used to use was a much heavier, stitched leather thing that became particularly heavy when wet. (We used call that type of ball a 'casey'.)
Many, many old footballers have been diagnosed with dementia. There have been studies in various countries which have led to heading being banned for young teams, as
@jennifer1967 says, but older players clearly still do. Many boxers get dementia too - they used to describe boxers as 'punch drunk' when they could barely speak after being in a fight.
It's not difficult to work out that hitting your head constantly is really not good for the brain....