I think there might be some universal feeling of "romantic attraction" however the response to said attraction might be different (culturally, personally, etc) which is what "romance" is.
As a romantic individual, I had what I considered my first crush in 5th grade. It was a kid I played Pokémon cards with. I just wanted to play Pokémon cards with him. But when I saw him playing Pokémon with his friends or other people, I got oddly upset. I didn't wail or throw a tantrum or anything...but it was just a solemn feeling. A rather sad reminder that I wasn't the only person he wanted to play Pokémon with. My thought process about him back then was pretty much "I want to play Pokémon with him forever".
Fastforward to age 16, I got into my second relationship (not counting my first because I don't think I really loved her). He was a guy that was into the same things as me and also enjoyed making art. It was a squish at first; I really wanted to get to know him as a friend and just spend a lot of time with him. And we did become friends! We talked to each other on a daily basis and joke around a lot. For me, this squish developed into a crush when I realized he was the only person I'd ever think about. I'd wake up thinking about him, wondering if he was waking up too, go about my business thinking about him, wondering what he was doing and hoping his day was going well, and go to bed thinking about him, hoping he has a great night and wondering if he's been thinking about me too. I would agree with some of the past comments that it's an obsessive feeling.
I think this is also different from a squish in the sense that whenever this boy joked about us "being cute together" or complemented me I quickly became flustered and at a loss for words. If someone I only liked platonically did this to me, I wouldn't have responded the same way.
If anything I said needs further elaboration or if any has any questions about (how I feel) romantic attraction feel free to ask me. I'll try to think up clear and concise responses.