Seneca was a Roman stoic philosopher and dramatist. He was unfortunate enough to be Nero's tutor and in 65 A.D. Nero forced him to commit suicide, after accusing him of taking part in a conspiracy to assasinate him.
Seneca wrote several plays and philosophical essays and was also a prolific letter-writer. One of his most famous essays tackles the shortness of life and argues that "life is long if you know how to use it". This particular essay has been very influential over the centuries, as many consider it to be a source of timeless wisdom.
Some interesting excerpts are:
"Why do we complain about nature? She has acted kindly: life is long if you know how to use it. But one man is gripped by insatiable greed, another by a laborious dedication to useless tasks...Many are occupied by either pursuing other people's money or complaining about their own...Some have no aims at all for their life's course, but death takes them unawares as tehy yawn languidly - so much so that I cannot doubt the truth of that oracular remark of the greatest of poets: 'It is a small part of life we really live.'...You are living as if destined to live forever; your own frailty never occurs to you; you don;t notice how much time has already passed, but squander it as though you had a full and overflowing supply."
"...he says, 'When will vacation come?'. Everyone hustles hi life along and is troubled by a longing for the future and weariness of the present."
Seneca apparently provides a solution for the above state of mind. He says:
"...the man who organizes every day as though it were his last, neither longs for nor fears the next day."
And about white hair:
"You must not think a man has lived long because he has white hair and wrinkles: he has not lived long, just existed long. For suppose you should think that a man had had a long voyage who had been caught in a raging storm as he left the harbour, and carried hither and thither and driven round and round in a circle by the rage of opposing winds? He did not have a long voyage, just a long tossing about."
More information on Seneca and his work: