OP, it sounds to me that you just lack dating experience, period. Love at first sight is a nice concept, but not actually a realistic one.
Most of what people describe as "love at first sight" or as a "crush" is that tingling rush of hormones/adrenaline/excitement. I see it as infatuation, and infatuation fades.
In your case, OP, I would just say go out with more girls, and see how you feel about them. I find it hard to believe that you haven't been at least attracted to some girls. Dating is about learning about people and seeing if you're compatible with them. I find it hard to believe that anyone can look at someone and think "wow, that person will be a good lifelong companion!" just from looking at them.
27 isn't old. So go out and get some experience!