Down the M4

In the second stanza it sound like his mother is telling him about time ageing him and how he says 'oh dear' or 'how funny' —> it's like he doesn't care because he's young. 

'Till I feel my hair turning grey' —> could suggest that he is only now understanding/appreciating what his mother has been telling him now that his is turning old. Alternatively, could be saying that his mother keeps telling him and he does not care and will continue not to care 'till I feel my hair turning grey'. 

'For I've heard that perishable one two hundred times before' —> suggests his mother keeps on telling him —> he's heard it all before.

First stanza could suggest that all of the people close to him keep dying. 

*contextual knowledge: Abse's wife died down the M4 in a car crash