"… staring down/All his young days into the harbour where/His ball went …" Do you think the boy has had the ball for a long time? Is it linked to the memories of days when he played with it?
Yes, the boy has had the ball for a long time. The phrase "All his young days" suggests that the ball has been with him throughout his childhood, making it a long-standing possession.
Yes, the ball is deeply linked to the memories of his days of playing with it. As he stares into the harbour, he is mourning the loss of his past memories. The ball represents his young days, and losing it brings an ultimate shaking grief because those cherished memories are now gone.
Explanation
The phrase 'All his young days' directly connects the physical ball to the boy's childhood memories. The boy's 'ultimate shaking grief' is not just for a cheap toy, but for the emotional attachment and memories associated with it. Staring into the harbour symbolizes him looking back at those memories that seem lost with the ball.