The word enlightened comes from the Latin prefix 'en' meaning 'in, or into' and the word 'lux' meaning 'light', so In or Into The Light
In a spiritual context there is extensive disagreement on what this means as it relates to the human experience. Therefore, when one considers themselves or another as enlightened, this is simply an opinion, based on interpretation of what that means.
Perhaps the most sensible way to approach this is to use the actual original and intended meaning of the word?
In that case, surely one who is enlightened would exemplify the characteristics of the The Light - the Ultimate Truth, the Eternal, the Divine One Reality?
Anyone who has been overwhelmed by joy, love, bliss, experienced absolute peace or the state of oneness, or a transcendental beingness merged with the indescribable may have tasted the characteristics of The Light - but is this one's every moment living reality?
Maybe that is the real test to apply?