Romans 8:6 says (ESV):
To set the mind on the flesh is death, but to set the mind on the Spirit is life and peace.Note that "flesh" here doesn't mean sex, but about things that are bound up with this world.
John Keating was right, in a sense - far too many people just drift through life, and we don't want to waste time - we have to be good stewards of our time as with everything else. But it's not for the reasons that he gives - that is, it's not because in 100 years' time we will be food for worms. From a Christian point of view, that's not how we see things. If our minds are set upon life and peace, then we are conscious of the fact that the day is coming when we will live for ever, and we will perhaps have the opportunity to do things that we can't even conceive of now!
So Keating's formulation of "seize the day" isn't the Christian perspective. Our minds aren't set on "death" - we don't seize the day because we will be dead tomorrow - because from a Christian point of view "to die is gain". Instead, our lives are set upon life and peace - our motivation is the fact that God has given us these things through his grace, and we are to use well what he has given us.