I think you might be on the asexual spectrum. Or just not ready to think or talk about sexuality. That's ok - neither is a bad thing.
But maybe some explanation might make it less uncomfortable for you: Most people don't "just" start thinking about sexuality and gender. There usually is some sort of feeling that sparks the whole process. And with most people it is realizing they are different from most other people around them.
When all the "other boys" are playing rough and talking about sports and cars and stuff and you just keep thinking, "that just isn't me... I'm not like that", you start to think about why you might be different. Maybe you're just not a boy.
Or all the other girls are starting to talk about guys and who is the cutest boy in class, but you can't find anything cute about any of them. Instead, when your friend said you should pratice kissing so you're ready for a date with a boy, you got really nervous because she might notice you have actually thought about kissing her for a while and it gives you goosebumps.
Situations like these make you wonder if it is really as clear cut as all the grownups have been telling you or if there is something they left out. Some people were born in the wrong body, some boys don't like girls and vice versa. Then you start to question the "norm". But the spark came from being different than others or feeling uncomfortable with what everybody expects of you. It didn't come from just thinking about what else there might be or reading about it on the internet. If you aren't different, if you are comfortable in your body, if you like the "opposite" sex, then you have no reason to start thinking about what else there might be.
I think that is why trans people - specifically ftm and mtf trans - are the first to notice, followed by homosexuals shortly after, asexuals and agender come later and bi- or pansexuals are the last to figure out. It is the most obvious to notice you are different from the others and don't like the same things and around the age of 12-13 is when it becomes more and more obvious there is a difference between boys and girls. And as long as you do feel like everything is normal you have no reason to start thinking about any of this.
And the fact that you're asking yourself whether or not you're homophobic is a good sign that you're not, btw. 😉