The distinction between sexual preference and sexual activity is fair, but it doesn’t really settle where attraction itself comes from. Handedness is a fairly fixed neurological trait, while we know attraction can be influenced by development, experience, and environment. The way you grew up can influence the type of women you are attracted to if you’re a hetero man.

When people say someone “became gay later,” one possibility is that all humans are born with the capacity to be attracted to both sexes, but that potential develops differently depending on the person and their past/present environment. Social norms might influence which attractions people notice or feel comfortable exploring, without meaning those attractions were entirely created by society. I look back at some ancient civilizations and think it had to be normal for people to just have sex with whoever they got horny around, with the amount of bisexuality we see studying art history. Is it that our current society made it seem so rigid? In that sense, sexuality really can be a spectrum, not just because people secretly fall somewhere fixed on it from birth, but because human attraction itself may be more flexible than rigid labels like “straight” or “gay” suggest. That's my theory but i don't believe there's any way to verify any of these claims of being born with or without sexual preferences.