I'm looking for a yaoi with a shorter seme such as "otona keikenchi" although not necessarily younger or with a huge age gap between the couple

There's a category tag for that, so you will find basically most recommendations there ...

Shorter Seme

"It's like love is a bonus in your life. Even without it, I'm just fine. I don't feel like pointlessly searching for it. You don't have to make yourself unhappy." (Ookami Shoujo to Kuro Ouji)

"Why does it rain?" - "To create drama." (Drops (Andou Yuki))

Thanks 😀 I'm kinda new to this site so I haven't got round to figuring out all the features in it