Age shouldn't be such a factor- unless the guys in question are really looking to settle down and start having kids. If that is the case, then for practical reasons they should be looking for someone in their twenties or early thirties.
Otherwise, there are plenty desirable/attractive women and plenty undesirable/unattractive women in every age group. It sounds like your ex was just trying to exploit your insecurities by pointing to these younger women. Besides, if a guy is only interested in dating 25 year old bikini models then he is probably not someone you would want to associate with.