yeah, since modern romance often ties “love” to physical desire, people tend to forget that in literature (considering this manhwa is an adaptation of a novel with the same title), first love can also be about pure admiration, appreciating someone’s beauty, or even a meaningful moment that leaves a deep impression without any sexual desire at all. And that’s exactly what we see here. It’s still valid to call it first love. You just need to understand that love can take many different forms.
if you still find it weird because Yuri was 25 while Xinlu was 12, that's exactly why pov matters. We get to see how Yuri himself describes those feelings, and based on what's actually shown in the story, they don't fit the medical criteria or law for pedophilia either
So a kid was his first love?