Get out the microscope, because we’re going through this poem line-by-line.
That age is best which is the first,
When youth and blood are warmer;
- The speaker divides life into several periods and says that the "first" (i.e., young adulthood) is the best because "youth and blood" are "warmer."
- "Age" just means "period of time" here.
- "Youth and blood" probably aren't literally warmer, but we often think of dead people as cold, so perhaps the speaker means something like "farther from death."
- Alternatively, "warmer" might even mean something like "more vigorous and healthy."
But being spent, the worse, and worst
Times still succeed the former.
- Youth is the "best" time of life, so the speaker says. Once it's gone, the "worst/ Times" follow.
- "Spent" means "used up" or "gone."
- "Worst/ Times" refers to the period after youth is "spent," so it most likely means old age or something to that effect.
- We're not quite sure what to do with "worse." We might have to supply syntax from the previous two lines and read the line as "being spent, [that age is] the worse [rather than the best]."
- That, however, doesn't make a whole lot of sense. It seems easier to read the lines as "the worse, and [even] worst / Times" will follow.