Learn philosophy whether you are young or old

Let no one be slow to seek wisdom when he is young nor weary in the search thereof when he is grown old.

For no age is too early or too late for the health of the soul.

And to say that the season for studying philosophy has not yet come, or that it is past and gone, is like saying that the season for happiness is not yet or that it is now no more.

Therefore, both old and young ought to seek wisdom, the former in order that, as age comes over him, he may be young in good things because of the grace of what has been, and the latter in order that, while he is young, he may at the same time be old, because he has no fear of the things which are to come.

So we must exercise ourselves in the things which bring happiness, since, if that be present, we have everything, and, if that be absent, all our actions are directed toward attaining it.

'Letter to Menoeceus' by Epicurus
http://classics.mit.edu/Epicurus/menoec.html