Consider above all else whether you’ve advanced in philosophy or just in actual years.
Seneca, Letters from a Stoic, XVI:3
Years mean nothing if we haven’t gained wisdom. And wisdom is worthless if it can’t be applied.
A useful definition of philosophy is that it is the practice of gaining wisdom by studying and consciously exposing oneself to the natural processes of growth and change in our selves, minds, society and the natural world.
For a fighter in the ring, victory or defeat is nothing more than the measure of the effectiveness of his training. Likewise for a philosopher, whole-hearted study of the inner and outer worlds in the easy times prepares him to apply philosophy in the harder times.
In this sense, wisdom is far from subjective and not at all open to interpretation. It is measured by the ability to keep a level head, stay curious, and thrive even under the worst of external circumstances.
Featured art source is unknown.
For more Stoic-style enlightenment, check out: