That's probably an overstatement, which is unsurprising if everyone saying it is a Japanese man. But a man who was actively looking for a wife would have no trouble finding candidates.
No, I don't think it is an overstatement. This even comes from the older generation. It is a very big deal in Japan the last couple of years. They say because of my social status and being an American, that Japanese women will be very blunt and forward to me about my interest in marriage even though they cannot be so direct in speaking with Japanese men.
All of my Japanese friends have wives that are 10 to 15 years younger than they are. In Japan, the ideal marriage is one in which the husband acts the role of the father, so the wife needs to be young to accept the male dominance over them. Women cannot be seen as dominant or equal in Japanese society, but they can be so with western men and they desperately want that (who can blame them). That is why they are rejecting Japanese men who are not adopting the western ways.