Imitations

This poem like 'Sons' shows a father son relationship. "My son and I" instantly shows this poem is a father and son relationship poem. The use of "other side of the glass" shows a division between him and his son, perhaps showing the old and youthfulness.  The idea of  "snowflakes" and "surprised April" offers an uncertainty in growing up as snowflakes don't usually occur in the spring.  This could relate to Larkin's 'First Sight' as again it brought a sense of un-expectancy and loss of hope.

"My son is 16, an approximate man" showing at this age he is still young and the idea of "whitewash" giving innocence or purity but he is also on the brink of growing up and maturing. "Eyes half closed" shows how relaxed he seems and that he has no care in the world other than going about his everyday teenage life and "listen to pop" and "dreams of some school Juliet" showing young love and fantasy.
Abse then goes to describe the sky which I feel refers to his son. The fact "despite a half blue sky" the idea he is growing and knows what he does, it also has "white blossom , whiter snow" he is still innocent and has a lot to come to terms with in life (naïve)

Like 'Sons' it takes the persona make to their childhood "till I'm elsewhere, the age my cool son is " remembering what his relationship with his father was like as he talks how he is now a "duplicate" of him.

The last lines in the poem talk of "two white butterflies" showing freedom and company, perhaps even longing for a loved one (his father) but the butterflies are "held each to each" they become in-separate but then "pass" as disappear as quickly as they came. This could reflect the relation with his father - that you are with them all your life and then take your own paths and eventually it ends and you "pass"