What do you think this dream of my Grandpa meant?
It was a dream about the inner child within you and also within your grandfather. Both of you had a magical time in the clouds, etc. This is normal. Even very old ppl have a child still living within them. I am so happy that although your grandfather has passed on, you were able to "play" with him in your dreams.
To see your dead sibling, relative, or friend alive in your dream indicates that you miss them and are trying to relive your old experiences you had with them. In trying to keep up with the pace of your daily waking life, your dreams may serve as your only outlet in coping and coming to terms with the loss of a loved one.