Seneca comes out guns ablazin’ right in the first few pages of On the Shortness of Life:
It is not that we have a short time to live, but that we waste a lot of it. Life is long enough, and a sufficiently generous amount of time has been given to us for the highest achievements if it were all well invested.
People are frugal in guarding their personal property; but as soon as it comes to squandering time they are most wasteful of the one thing in which it is right to be stingy.
Time is monotonically increasing - it will never go down from the point it is right now. If you want to accomplish something, start now. There is no such thing as too late. As the Chinese proverb goes:
The best time to plant a tree was 20 years ago. The second best time is now.