I am a top only.
My opinion is that being a top just means that you do not enjoy in any way to be penetrated, and only like to penetrate.
Aside from that there are other preferences and behaviors that can be tied to being a top, but arent necessary. That includes not liking sucking dick, being dominant, being distant, not kissing and generally displaying a "straight" behavior. Until you get to the ultimate stereotype that combines all these.
For me its a matter purely of biology. I have tried many times to be the receiver, with different guys but I just dont get any satisfaction mentally or physically. Even when it doesnt hurt, its boring me out. Sucking dick, I dont mind it but it also bores me out.
Oh, and I do like to kiss of course. Its a big turn on.
So yes you can be a top only.