Primo

middle aged AND OLDER***

i’ve been on the search for the same thing. one is just a buff bottom. the others are aren’t really fem tops just not typical tops.sorry these are the closest things i’ve read recently but i hope you like them!
https://www.mangago.me/read-manga/their_love_is_too_much_for_reality_tv/

https://www.mangago.me/read-manga/be_my_bottom/

https://www.mangago.me/read-manga/i_m_sorry_but_daddy_is_my_type/

not exactly a femboy x old man manhwa but try "the taming"
the uke's VERY buff and is much bigger than the seme, plus, he's nonchalant. the seme's shorter and skinnier (except for his dih of course ╮(￣▽￣)╭). their chemistry is insaaaaane, however, and the plot's pretty interesting too.

Try "Plaything"
Author: POTION, TR
Lemme know if it's atleast similar a bit to your dreams..
There's also the famous "Indomitable"

"Indomitable Champion"

i’ve read both of these! plaything is one of my faves tho sayan is more of just a pretty and ethereal man and not really femboy ヾ(❀╹◡╹)ﾉ~

tysm i’ll check it out

THANK YOU hopefully one day we will find exactly what we’re looking forヾ(☆▽☆)