I thought I bookmarked it and I can't find it. From what I remember its either a one shot or a side story. It's about an older man with light hair and glasses going to an island/jungle in search of a banana(?)/fruit that will grant immortality. That or its a miracle fruit. And while there he stays with a younger man with I think tan skin. I know it was not an older manga. The art style seemed newer.

Unfortunately, that's all I remember.

Thank you in advance.

All this time looking and I found it immediately after making this post.

Goriyou wa keikakutekini
Ch. 5