1. When the poet says to his father "Curse, bless me now with your fierce tears, I pray"= He basically summons the last of the strength of his father to be spent at that very last second of life and, by default such last bits of energy mean that there is still life and energy inside of him
2. "Old age should burn and rave at close of day"- fight until the end, breathe until the last bit of air is left; keep going even if you are about to be finished.
3. "Good men, the last wave by, crying how bright
Their frail deeds might have danced in a green bay"- When people find out their lives are about to end, they cling on to every thing they had not done, or regret for not attempting and many jump at that very moment and get things done- therefore, they are also fighting until the end.