From Seneca’s Epistles (13.16)
But now, to close my letter, I have only to stamp the usual seal upon it, in other words, to commit thereto some noble message to be delivered to you: “The fool, with all his other faults, has this also,—he is always getting ready to live.” Reflect, my esteemed Lucilius, what this saying means, and you will see how revolting is the fickleness of men who lay down every day new foundations of life, and begin to build up fresh hopes even at the brink of the grave. Look within your own mind for individual instances; you will think of old men who are preparing themselves at that very hour for a political career, or for travel, or for business. And what is baser than getting ready to live when you are already old? I should not name the author of this motto, except that it is somewhat unknown to fame and is not one of those popular sayings of Epicurus which I have allowed myself to praise and to appropriate. Farewell.
Sed iam finem epistulae faciam, si illi signum suum inpressero, id est aliquam magnificam vocem perferendam ad te mandavero. “Inter cetera mala hoc quoque habet stultitia: semper incipit vivere.” Considera quid vox ista significet, Lucili virorum optime, et intelleges, quam foeda sit hominum levitas cotidie nova vitae fundamenta ponentium, novas spes etiam in exitu inchoantium. Circumspice tecum singulos; occurrent tibi senes, qui se cum maxime ad ambitionem, ad peregrinationes, ad negotiandum parent. Quid est autem turpius quam senex vivere incipiens? Non adicerem auctorem huic voci, nisi esset secretior nec inter vulgata Epicuri dicta, quae mihi et laudare et adoptare permisi. Vale.
Depending on your interpretation of what Epicurus meant (and there’s no confirming context surviving) and what Seneca wants him to mean this potentially goes much against the spirit of Socrates’ advice in today’s earlier extract from the Laches.