well yes it is imo.
The problem is, not just the dying early, and the probability of him being infirm while the child is relatively young, but there is no way that he'll be around to be a grandfather. There's no way he'll be around much into the child's adulthood, and I've discovered now that my young adult children need me just as much as they did before. I also get to enjoy my adult children I get the grown up relationships, to see how they are developing. To watch them go off into the world.
And your partner however young at heart he is, simply won't have the energy of a young person. And in fact, at this stage in his life, does he really really want to do all of that drudgery, sleeplessness, soft-play shit? really? I did have my last child quite old, but still, I'm so pleased now that I can concentrate on doing fun stuff. I'm getting to go off on weekends with my older children, go cycling, climbing and sailing. I wouldn't be able to do that if I was in my 70s. No matter how fit I was.
And the other thing is that it is massively embarrassing to a child to have an aged parent that looks like their grandparent.
From your perspective, assume you won't have the support for the whole time you are a parent. Assume your OH won't be as energetic, or as in touch with the kids, or as interested in all of that stuff. And that's keeping the whole death/disability stuff out of the equation. It's just a matter of fact.
So yes I think it is too old.