What does "too old to relocate" mean? For me and my relationship and my values and the culture of my family (which is to say that there's no value judgment here and every relationship is different), if I was grossly unhappy, coming off a cancer diagnosis and treatment, and loathing where I lived, if my partner choose caring for his parents over caring for me, that would be incredibly painful and incredibly telling.
And if all his parents have ever wanted is a grandchild, then it seems they want that more than they want to not move. So, propose that everyone gets what they seem to want--he gets to continue hands-on care with his family, his parents get a grandchild, and you get to move. It seems like right now, he wants everything. What's he sacrificing in this relationship? or are you doing all the sacrificing while he gets to coast on a life that works for him and not for you? If that's the case, are you willing to call him on that? What is he willing to flex on? What can he change to meet you partway? What are you willing to flex on to meet him part-way? (It sounds like that might be having a child, and if you are genuinely okay with that, great, as long as it's a thoughtful choice on your part.)