Truth is the daughter of time, not of authority.
Some books are to be tasted, others to be swallowed, and some few to be chewed and digested: that is, some books are to be read only in parts; others to be read, but not curiously; and some few to be read wholly, and with diligence and attention.
Read not to contradict and confute; nor to believe and take for granted; nor to find talk and discourse; but to weigh and consider.
Old age, which is dreaded by all men, is to me the sweetest and most pleasant period of my life.
You cannot stay on the summit forever; you have to come down again. So why bother in the first place? Just this: what is above knows what is below, but what is below does not know what is above. One climbs, one sees. One descends, one sees no longer, but one has seen. There is an art of conducting oneself in the lower regions by the memory of what one saw higher up. When one can no longer see, one can at least still know.
Hang on to your youthful enthusiasms — you'll be able to use them better when you're older.