Hi

https://www.mangago.zone/read-manga/tonari_no_metaller_san/
Above one has case of suffering from similar and really close call to hypothermia.... While for age gap ...I ain't certain about numbers but yes the following has a huge gap like the generation gap
https://www.mangago.zone/read-manga/love_nest_minaduki_yuu/
https://www.mangago.zone/read-manga/joou_to_shitateya/
https://www.mangago.zone/read-manga/shishi_ni_hire/
https://www.mangago.zone/read-manga/how_sweet_is_a_sugar_daddy/
https://www.mangago.zone/read-manga/koi_ga_ochitara/
https://www.mangago.zone/read-manga/kitto_oujisama_ga_nante/
https://www.mangago.zone/read-manga/on_doorstep/
Maybe you might have already read these...anyways if you get something new to read. It'd be wonderful for you. Adiós

Yes I have some old mangas I don't know if u comfortable with this one but this chp story contain age gap -.
https://www.mangago.zone/read-manga/recipe/an/recipe-chapter-3.html/1/

This one is cute like 20 years age gap -
https://www.mangago.zone/read-manga/himono_tokodoki_shanairen_ai/


It's also age gap like around 10 -
https://www.mangago.zone/read-manga/bokura_ga_koi_wo_ushinau_riyuu/


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

It has over 20 years age gap -
https://www.mangago.zone/read-manga/katsubou_no_manazashi/

This one is 20 or could be less cuz seme is 39 but uke is collage student-
https://www.mangago.zone/read-manga/hana_wa_saku_ka/

Yes this one has over 20 years age gap cuz they r father and son and real one -
https://www.mangago.zone/read-manga/not_equal/

Sorry I didn't see your 30-40 age gap
╥﹏╥ I only suggested 20 years gap but first one might be 25+ age gap.

20* no I m correct why my autocorrect actiong weird aghhhh