Success should not be measured by the amount of money in your bank account or the size of your house. It should not be measured by the prestige of your job or the luxuriousness of your vehicle. Success does not depend on the attractiveness of your spouse or looking ten years your juniour.
Instead, measure success in the number of lives you've made a difference in. It can be measured in the beauty of your actions and the things you've experienced. You can only truly have success once you have truly lived.
I really like Ralph Waldo Emerson's take on this in the following passage:
To Have Succeeded
by Ralph Waldo Emerson
To laugh often and love much;
To win respect of intelligent people
And the affection of children;
To earn the approbation of honest critics
And endure the betrayal of false friends;
To appreciate beauty;
To find the best in others;
To give one's self;
To leave the world a little better,
Whether by a healthy child,
A garden patch,
Or redeemed social condition;
To have played and laughed with enthusiasm
And sung with exultation;
To know even one life has breathed easier
Because you have lived...
This is to have succeeded.