Distant Neighborhood (Haruka na Machi e) by Jirō Taniguchi

Trying to rucuperate from his hangover, the a 50 year old man takes the wrong train to work.
Instead hops on one heading towards his childhood village. He takes advantage to stop at his

mother's grave. The cheerless old man awakes in a moment of blankness. Little by little he stands up only to know he made a leap into the past. The aged fellow just found himself in the body of a fourteen year old. His body.