while they are becoming "old" and are now grandparents, you and DH are embarking on a youthful journey for a new baby! I don't envy folk who get married so young and have kids so young. I'm glad I waited until I was older....there were other things to experience first.
The part that is sad is that your parents will not have as much time with them, and you will not have as much time with the child. My Mom is early 70's, and I'm due to have #1 in March. I'm already calculating how long this child will have a G-Ma and a Ma.
It's rough, but we are so blessed to have this technology available to us. Good Luck!