Responses
Spoiler alert
I read the novel and ml has undergone rejuvenation becs he has strong enemies waiting for his death. The ml's life story is also very tragic. He lived his life for revenge. So I can confirm that he didn't actually lived his life to the fullest. But at the end after falling in love with the mc he is living a fulfilling life with mc as his lifeline.
I have no issue with the age gap since I've consumed an immeasurable amount of xianxia/danxia/whatever-xia BL where the immortal venerable bottom is always... well... at the age where one almost reaches immortality (some use 100+ yrs, some use 800+).
BUT SINCE THEY MENTIONED A SPECIFIC AGE (80ish?) AND AGE(?) REGRESSION, ALL I CAN THINK OF IS: "damn... grandpa is so horny as soon as he got his young body/vigor back"
BAHAHAHAHA no hate, no shame. I'm still reading, but I'm calling him grandpa the entire time while at it bec I can't remove 80 yrs old in my head (doesn't help that unlike cn danmei where they always say the immortal cultivates in a secular way, ML clearly lived his life to the fullest).
note, jic ppl come at me: My age gap comment refers to when both parties are actually adults (which is ofc always how it is in this kind of genre (kr or cn alike)), and does not apply to where one of the main characters is so obviously a minor. In stories like this where there is cultivation, age really is literally just a number since their cultivation takes up most of their years and they have less time to bother with "mortal" things like vices and romance. So yes, age gaps are rarely an issue in these stories (unless one is a minor).