Dengeki Daisy? But their age gap can be kinda off putting. Nothing weird happens from what I read and they were sweet
https://www.mangago.zone/read-manga/sesame_salt_and_pudding/ (probably the best example, they're so cute)
https://www.mangago.zone/read-manga/rather_than_the_son_i_ll_take_the_father/ (he looks younger than he is, but he has an adopted son her age)
https://www.mangago.zone/read-manga/reemployment_life_with_an_unsociable_untalkative_magician/ (he's a handsome grandpa lmao)
https://www.mangago.zone/read-manga/i_woke_up_in_a_fantasy_world_as_a_young_lady_and_fell_in_love_with_my_ex_fianc_s_grandfather/ (another handsome grandpa)
https://www.mangago.zone/read-manga/doppio_senso/ (smaller age gap but still a bigger age gap than usual)
shojo mangas w age gap couple?? but like not groomy or creepy yk? just a sweet girl and a older man, healthy relationship !! please and thankyouu (づ￣ ³￣)づ