How old is too old to have kids, in your opinion?

I’m 31, my husband is 51, and lately I’ve been feeling some baby fever. For the record, kids aren’t a must for me, I’m genuinely happy with or without them, but I think it would be nice to experience that journey. My husband is hesitant, though. Even though he’s very healthy, active, and energetic, he feels like having a child in his 50s might be too late. He also already has a 27-year-old son, and he worries that the big age gap between siblings would feel strange.

I guess I’m just looking to hear what others think about this situation.