Can i ask.....What is normal???
if its something you like....Why are you regreting and denying this part of yourself.
seriously consider if it's more of a material think you are tapping into rather than a relatioship with someone closer to your age. the relationship if you ever go to that is very different than the growing pains of people whoa re younger and less mature.
It's doubtful you understand them untill you try and operate at their level which you can't. See if youc an talk to a professional to see if your heart is really in the right place.
You're only 20yrs old so please don't be offended when I say that you're just not "sexualy mature" yet and that is probably the only problem here. You see it's just that you have been around "mature" women for the majority of your life so far, so it's just "misplaced security" in a certain type of woman so you are finding yourself attracted to married women because they represent what you consider to be the perfect woman. They will nurture you, take care of you and offer you that security you desire so much.
As far as the fantasies go they are just that-"fantasies"- and nothing more. Your thoughts don't define you only your actions do, so until you act upon these thoughts don't let these thoughts control or define who you are as a person.
In the back of your mind you are just "affraid" of "girls" your own age and this can be overcome by simply developing healthy friendships with girls your own age. Part of growing up is accepting the rejection you will face from women and that could be what you're avoiding. Don't avoid things in life but learn from older men how to deal with it.
Also, I would recomend finding a female relative that can help "teach" you about women. You know, a cousin your own age.