Halp

https://www.mangago.me/read-manga/an_old_man_from_the_countryside_becomes_a_swords_saint_i_was_just_a_rural_sword_teacher_but_my_successful_students_won_t_leave_me_alone/
Its not isekai but the MC is middle aged..

Iz not it. But thank you for the nice find.

Ah then I'm sorry I can't help you! You could try asking on the isekai subreddit, theyre more knowledgeable

‘Ygret’? i cant paste the link tho