You should always be authentic.
I think you're confusing authenticity with your habitual nature. Who you are, how you perceive and react and behave on a daily basis as default is simply the ledge on the mountain you are currently at. You can be authentic when you override this default, it's called growing.
In my view, inauthenticity is when you do something that you don't actually desire to, and strangely enough that is commonly the very thing many people do habitually, perhaps out of fear, as part of their 'authentic' identity.
When a man sees a sexy woman and wants to say hello, but doesn't, this is him blocking his true nature and not being authentic.
As far as different types of women go, first be curious about them, and non-judgemental, and even humble toward your lack of knowledge, and you will find yourself enjoying kinds of interactions you've never had before, and feeling your definition of yourself expand.