"If you presume that you will live long, and that you will be able to do your practice later on in life, you clearly do not have a strong understanding of the uncertainty of samsara, and of impermanence.
Only when you have a strong understanding, will you not want to waste a moment of your precious human life. You will become like a person who has just realised that the building they are in is on fire. You would get out while you still have a chance."
~ Chamtrul Rinpoche