For a first baby? Over 50 is too old as a knee jerk reaction, but there will be outliers who were just super late bloomers or late to realise they wanted to have kids who are great dads.
However- don’t think men who have adult children should be having newborns with younger women though, even if they are under 50. That ship has sailed, and it’s unfair on their adult DC. I’ve known a few people (aged between 25-38ish) whose dads shacked up with a woman their age and had a new baby. In all situations, the relationship never recovered.