Wow. Why am I constantly surprised by the puritanical streak that runs through this 'liberal' website?
OP, I tend to agree with the thoughts you seem to want to have. I think you are angry and hurt because you were surprised and just have no place for this new information. If it won't fit in your worldview then you reject it. The hurt and anger are like retroactive reactions to the rejection.
If your friend came to you one day and told you that he met some older lady in a random encounter and ended up in bed, you wouldn't feel this way. You might make a joke or two at his expense related to her age but mostly you'd do what all guys and do give him the verbal equivalent of a high-five. There's nothing wrong with him having sex with an older woman. If he's old enough to have sex and she's old enough to have sex, that's the end of it.
Alternatively, if your mom started dating a guy who was younger than her... where do you draw the line and say that you object? If your mom was dating a guy who was 30, would you put your foot down and tell her it was wrong? What about 27? As you think this through you start to realize the line is pretty damn arbitrary. As far as the law is concerned, the line is 16 or 18 depending on where you are. Everyone has their own personal line, though, and it varies.
Now try that exercise again and reverse the genders. What is your reaction to a 42 year old man with an 18 year old girl? If it is different, why is it different?
Now remove the dating aspect and imagine a 42 year old woman, feeling a little lonely or not the best at dating, hires a high-end escort. Does his age matter? Now, again, reverse the genders and think it through. Is there a combination where consensual sex is wrong?
You begin to realize that there aren't any really good answers that you can say ought to apply to everyone. There are no generalizations in this, there is just what you are comfortable with, what you might do, what you might approve of.
I understand your hurt and your anger but I think you are on the right track with questioning them. You are bumping into some assumptions that you didn't know you had and your instinct is to find a rationalization for them. Follow that rational mindset where ever it leads you and if it turns out your assumptions were wrong, have the bravery to get rid of them.