My dad had me at 54 0r 56, cannot quite remember. My mother was still very young then, 30 or 31 (cannot be bothered to do the math).
I think, however infair this may sound, that if the father is older (as long as it is not excessively) but the mother younger, that it is usually ok.
The problem is that how healthy the woman is physically plays a huge part in how healthy the baby is and how many complications may arrise during pregnancy.
The only thing with this scenario IMO is that it isnt fair on the children or the wife if the father is excessively older and unable to have the same relationship with his children that a younger father could have.
Also, if he does die, the mother may be around but the children have lost a parent and it is harder all round for the mother to raise them IYSWIM.
My father was very fit and healthy for his age so that was never an issue, but it could be for others.
But then I do wonder about women who have babies in their late 30s and early 40s as it also carries risks, which I have seen first hand. Nowadays it is the norm, but without modern medicine and a change in socio-economic issues, would not be considered as a relatively OK thing to do. It is only recently that it has become more acceptable as womens social roles change (but do correct me if I am wrong).
I know a lot of women, including myself, in my extended social circles (friends and friends of friends for instance) who have chosen to have babies in their mid twenties. It seems some young women are now opting to have a baby and then career to avoid being an older mother.