The "golden shovel" could make you think of death and grave digging. Why is the shovel "golden"?
Lurk late. (line 3)
If any of the lines can be tied directly to the final prophecy, "die soon," we think it's this one. A person who "lurks" generally doesn't want to be seen by other people. It's a form of hiding. Why don't the pool players want to be seen late at night? Or do they care?
We Sing sin. (lines 4-5)
OK, so maybe you could tie their celebration of sin to the last line as well. However, the poem doesn't mention any particularly terrible sins: drinking, carousing, and skipping school.
We Thin gin. (lines 5-6)
Perhaps it's alcohol that's will kill them. Maybe Brooks is predicting lives of alcoholism for these young men based on the fact that they are drinking and have left school. One of the reasons this poem is so powerful is that the speaker is able to create a vivid and provocative image using very little language.
We Die soon. (lines 7-8)
The speaker says, "Die soon," instead of the more conventional "Die young." How is "Die soon" different? How soon? Is she referring only to these seven young men, or a larger group of people?