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.
I always wondered what are the movtive of men who are madly in love with an older women or a younger women. So, being a professor I searched. I found a study, published in the Journal of Couple and Relationship Therapy, that showed couples thought their age difference mattered more to the outside world than to them, and that the men were more strongly drawn to the relationships at the start because of physical attraction. Underline "physical attraction." Men are visual creature. So a man that is madly in love with you be it younger or older may not be looking at your character, talent, heart, and soul but at your beauty. A more interesting experiment would be to put some photos up of yourself without make-up looking plain. Then see how many emails you get. I would venture to say it would be few. If so, you need to ask yourself if a man is after you as a person or you as a beautiful trophy? I believe one leads to true happiness and the other false happiness. Good luck.