Our little grand daughter sees no age barrier when she looks at her grand parents. To her we are playmates capable of pushing the swing for hours, of leaping over her "long jump barrier" in the garden, and able to chase her round the house and read endless stories. She sees no reason why we can't play with her just the same as her little nursery companions do.
So to us putting the GRAND in grand parenting means being there as her friend, protecting her from outside nasties as much as possible, and letting her grow and develop at her own pace with a little bit of encouragement here and there.