Sexual orientation option

iKathness There is no switch to set gender preferences globally.  Flirting has always been a bit overboard in the game and there are certain things that you can do to make it worse.  The Eco Lifestyle Free Love NAP makes it more prevalent so not using or repealing that one can tone down some of it.  What traits and likes and dislikes you give a sim also can affect it.  But with the exception of the Discovery traits and the Likes/Dislikes popups you get, you have to set or change those in CAS on a sim-by-sim basis.  The attractiveness system also affects it.  Sims that are unattractive to your sim and vice versa slow some of it down.  Again, that comes back to how and what turn ons and turn offs a sim is assigned.  The fewer turn ons and turn offs you assign you use will make a sim less attractive to fewer other sims although the downside is that it makes it harder to find a compatible mate as there are fewer sims they are attracted to and fewer sims that will be attracted to your sim.  If you don't set any turn ons, or if you set too many, you will get a lot of sims attracted to your sim and more flirting too.  Unattached single sims can get the Single and Lovin' It Lifestyle as well if you direct your sim to do a lot of romance socials and that can play a part as well.  And as you know, how your gender preferences are set also affect it.   So, lots of ways you can affect things that can make flirting more or less prevalent, even for the sims you are playing at the time.    

To control it a bit other than through the CAS settings, you can play with autonomy off which stops your active sims from flirting unless you direct it but played sims in non-active households used as NPCs and NPCs will still flirt with your sims.  There are also several mods that I know that will allow you to control it a little better if you are a mod user.  There is nothing that I know of that will shut it down completely.

Hope this helps.