jeha

https://www.mangago.zone/read-manga/wadatsumi_no_yometori/

They're both old (immortal) but the Top looks younger because he is a mermaid.

https://www.mangago.zone/read-manga/on_doorstep/

For u bbg ♡

https://www.mangago.zone/read-manga/boku_no_omawarisan/ and the author's other works

love so pure

when the killer falls in love/ killer crush

my guildmate next door

under the green light

https://www.mangago.zone/read-manga/an_old_bottom_wants_to_be_loved_obsessive_sex_with_a_younger_doggy/

https://www.mangago.zone/read-manga/boss_bitch_baby/

Here list of younger semes-
https://www.mangago.zone/home/mangalist/1787219/

https://www.mangago.zone/home/mangalist/2311471/

My old man list
https://www.mangago.zone/home/mangalist/2558323/

Some that match what you're looking for
Coming and Come Over by Niyama (honestly most of their work is what you're looking for)
Boku no Omawarisan
Joou to Shitateya
40 Made ni Shitai 10 no Koto
Old-fashioned Cupcake
Kitto Oujisama ga Nante
Mujaki na Wanko to Nekokaburi
Ii Ko ni Dekitara Hometekure
Ore no Buka ga Eroi Mousou wo Yamete kurenai
Aitte Yatsu o Oshiete Kure yo
Yutori Shain ga Kachou no Karada, Nerattemasu!
The Man Next Door
SHOCK! My Favorite Online Beauty Streamer Showed Up at My Work, and What Happened Next…
Love-Shower for the Twisted Flower

GUYS THANK YOU

I know one! And it's manhwaZ. . Com but I don't know if u will like it. It has some popped up ads(〜￣△￣)〜

Nvm bro it's gone I think... see it for urself ♂