I cannot tell you and I’m sorry that he has gone. We all, in our hearts, want our Grandparents to live forever. That’s how it should be. However some of them can be mongrels and nasty characters and few miss them when they go.
To have that good Grandad must have been great.
Nobody can tell when his or her time is up or why.
SO ... make the most of them while they are here and say, “thank you” to God for them every day and love them.