Sorry, I meant to ask "is he a fussy eater".
This type of behaviour is seen in some children with autism. But you don't say anything about that. So is your grandson a typical child in all other respects ie. language and communication and social interaction etc?
If he is have a look at sensory integration disorder. This behaviour is linked to that, and SID is frequently a part of autism. However you can have SID without autism.
Do any of his senses appear over or under sensitive? The type of behaviour you mention is typically seen as sensory seeking ie. one or all of the senses are not getting enough information and so this behaviour starts. What is his sense of smell like. Is he a fully eater or will he eat anything.
Well the fingers I could say would be a little habit I am not so sure about the gate railings, Have you asked him why?