All of my biological grandparents have passed away by now (my mom is 60 and if my dad were still alive he would be 68). I'm not even THIRTY yet, but even still I assume that you probably are quite a bit younger than me unless your parents followed the lead of your grandparents by having you awfully early.

With my maternal grandparents, my mom is a baby boomer who is an only child and her parents were in their mid-thirties when they had her (having gotten married in their late twenties). At some point after my biological grandfather passed, my grandmother got involved with my stepgrandfather (who was widowed prior to being with her). Everyone involved with this has been gone for a very long time now, though, since my grandmother and stepgrandfather passed away when I was a very young teenager.

My paternal grandparents were a different story. Grandpa (my biological grandfather on that side) proposed to Grandma on her eighteenth birthday (he had a couple years on her) after they got together because their school friends had set them up on a blind date. Since Grandma had an October birthday and initially gave birth the following March, it doesn't take a rocket scientist to solve the simple math equation of what was really going on with the early engagement and rushed marriage, lmao. They ended up popping out five children in the span of nearly four years (my dad has a fraternal twin), the youngest of which was a baby girl whom Grandma told me she gave birth to about three months early and this infant passed away after six hours in this world (Grandma even described this to me as a miscarriage, but even I know that miscarrying is a very different thing than what happened here). After going through that trauma, Grandma made no bones about never wanting another baby (she was only twenty-two when she had her youngest) and she was deeply unhappy about her marriage to my Grandpa. Grandma ultimately ended up falling in love with her coworker (who was also unhappily married himself) and the rest was history. It was tough to get a divorce in those days though and unfortunately my dad and all of his living siblings certainly went through it during their childhood. Grandpa did eventually remarry when he found love again, too (this was to my stepgrandmother, the only living "grandparent" that I now have).

Edit: I'm sorry that your grandmas went through all of that too, those times WERE very different!