I never liked Freud...
And no, I never wanted to have sex with my mother
I never had any desire to kill anyone.
(And I don't want to kill anyone in the future.
)
I think we all have an instinct of reproduce each other and we are more
attracted by youn_ger woman because chances are much better that they
can give life to healthier babys than older woman.
Another reason could be, what we think is beautiful and what not.
As Josiah mentioned, at the age of 15->20, human beauty tends to peak.
And we all like beauty. If we can afford, we (would) buy/drive a beautiful
car, buy/build a beautiful house. Many want to wear beautiful clothes...
We love the beauty in all things... see beauty in nature too...
Compare a beautiful butterfly with an ugly dark moth...
All the best,
Calahan