Perhaps you are reading the wrong authors? Here are a few I love, and reread sometimes, that I don't think fit your description:
http://www.mangago.zone/read-manga/soryanaize_darling/
http://www.mangago.zone/read-manga/tokyo_crazy_paradise/
http://www.mangago.zone/read-manga/cutexguy/
Yoshihara Yuki is truely funny, http://www.mangago.zone/read-manga/haa_haa/ gets me in stitches everytime.
Well, if you say it like that, it sure is the same, but I started reading yaoi because I found the specific details in the plot and characters more interesting than some shoujo. '^'
It's not a matter of the general plot, but more of the details that makes a story better.
Also, I don't think shoujo and yaoi target a specific age range either. '^' Some are more fluffy and others are more mature. Really depends on what you're looking for.
I do understand that most shoujo is targeted at younger girls, while yaoi is targeted for the older section, mostly females, but honestly do they not have the same plot?
Shoujo is mostly the same as yaoi in my eyes. just a homosexual relationship.
A female falls in love with a cooler male.
They become friends
They realize they like each other after a event
They get together.
Yaoi might be more mature then shoujo, but I still see the same pattern
A male falls in love with a cooler male (or weaker girly male)
They become friends
A event happens, (usually forced love making) and they realize they like each other
They get together.