I have some friends with that kind of age gap and it doesn't seem to be a problem, for now anyway. A relationship is a relationship whatever the ages involved, some work/last some don't.
At least with a woman in her forties you know what you are getting unlike someone in their twenties/thirties who is still maturing.
I don't see it as a problem in compatability terms. I suppose really it is just the having children thing that concerns me.
She has either had children or now knows she is unlikely to.
Few men of my aquaintance actually want children ~ they accept them as an inevitable consequence.
Anywhoo ~ it really is none of your business.
My great grandmother was widowed. As soon as her children were had left home she knocked 11 years off her age and married a man 25 years her junior. Bet he got a shock on the wedding night