I feel like I have not yet mourned the deaths of my grandparents, which occurred at the ages of 20, 22, 30, and 31. My T said I may have already processed my maternal grandfather's death without really mourning; simply because of the circumstances of his death (cancer all over his body), it was a relief. I probably didn't really mourn my paternal grandfather's death because I really didn't know him. We haven't discussed my grandmothers yet.
Everybody processes things differently. Don't feel bad, granite.