A antiga linha de pó , de Richard Parker
Brian goes for a ride on a mysterious steam train that takes him back into his childhood.
...Richard Parker's The Old Powder Line (1971), a story of journeys from a strange extra platform in a station, where a steam train takes people to their pasts. On one trip teenage Brian meets himself as a baby, and finds his mother half-recognising him.
The time traveller cannot cross the frontier of his age and remain bodily whole, a problem faced when Brian, as a thought-shape, goes back to rescue Arnold from the 1920s and then returns for someone old enough to go back physically. This scientifically arranged chronoclasm is supplemented by astral-plane projection: the comatose body of Arnold, in hospital, shows the very symptoms of Arnold-in-the-past trapped in a tunnel.