Read Seneca's perspective on being old:
age has done no damage to my mind, though I feel its effects on my constitution. Only my vices, and the outward aids to these vices, have reached senility; my mind is strong and rejoices that it has but slight connexion with the body.
I'm drawn to that last part of the quote: "my mind is strong and rejoices that it has but slight connexion with the body" When I read that, and taking Seneca for his word, he means that his old body isn't really driving him anymore and that his mind has more sway over the body. This is an important note - your body craves things; it has desires. But your mind knows what's best for you. Do you give in to the body's desires or does rational philosophy, in your mind, call the shots?
Next he gets into whether he owes this result to old age or to philosophy.
how much of this peace of spirit and moderation of character I owe to wisdom and how much to my time of life; it bids me distinguish carefully what I cannot do and what I do not want to do.
Said differently, how much of your lack of desires are due to simply becoming old versus you having done the hard work to educate yourself in the proper management of desires?
Seneca proposes a test to find out.
The showing which we have made up to the present time, in word or deed, counts for nothing. All this is but a trifling and deceitful pledge of our spirit, and is wrapped in much charlatanism. I shall leave it to Death to determine what progress I have made. Therefore with no faint heart I am making ready for the day when, putting aside all stage artifice and actor's rouge, I am to pass judgment upon myself, – whether I am merely declaiming brave sentiments, or whether I really feel them; whether all the bold threats I have uttered against fortune are a pretence and a farce. Put aside the opinion of the world; it is always wavering and always takes both sides. Put aside the studies which you have pursued throughout your life; Death will deliver the final judgment in your case. This is what I mean: your debates and learned talks, your maxims gathered from the teachings of the wise, your cultured conversation, – all these afford no proof of the real strength of your soul. Even the most timid man can deliver a bold speech. What you have done in the past will be manifest only at the time when you draw your last breath. I accept the terms; I do not shrink from the decision.
And here is a different translation of the same passage, to help the meaning become a bit clearer.
All that I’ve done or said up to now counts for nothing. My showing to date, besides being heavily varnished over, is of paltry value and reliability as a guarantee of my spirit. I’m going to leave it to death to settle what progress I’ve made. Without anxiety, then, I’m making ready for the day when the tricks and disguises will be put away and I shall come to a verdict on myself, determining whether the courageous attitudes I adopt are really felt or just so many words, and whether or not the defiant challenges I’ve hurled at fortune have been mere pretence and pantomime. Away with the world’s opinion of you – it’s always unsettled and divided. Away with the pursuits that have occupied the whole of your life – death is going to deliver the verdict in your case. Yes, all your debates and learned conferences, your scholarly talk and collection of maxims from the teachings of philosophers, are in no way indicative of genuine spiritual strength. Bold words come even from the timidest. It’s only when you’re breathing your last that the way you’ve spent your time will become apparent. I accept the terms, and feel no dread of the coming judgement.
In the above passages, I italicized parts which I find impactful to myself.
So there it is - it's a mental exercise to test yourself if you are ready. Can you close your eyes and pretend to think if you are ready to die. Will your life reflect the actions your words espoused? What will the score show when time runs out? In one column will be all the times you professed a wise bit of advice. In the other column will be the courageous, just, wise actions you have carried out. Which will have more? I like to think I've lived a good life and that I've tried to act wisely. I know I am not perfect - no where near it. I do talk and write about it a lot; with the hopes that some of this will sink in and manifest itself through my mind and body in the real world.
Epicurus advised people to think on their death too. And if death is too morbid to think on, then alter the thought a little. Death is just a bit of traveling from one place to another; with some liberation thrown in.
"Think on death," or rather, if you prefer the phrase, on "migration to heaven." ... When we can never prove whether we really know a thing, we must always be learning it. "Think on death." In saying this, he bids us think on freedom. He who has learned to die has unlearned slavery.