One possibility is that GP is thinking that &quot;life expectancy was 25, so 20 means you&#x27;re an old geezer on the deathbed.&quot; Alternatively, it may also be a reference to the extreme youth of Alexander the Great, who became king of Macedon at age 20 and proceeded to put down a Greek rebellion and then conquer Thrace, Persia, Egypt, Bactria, cross the Hindu Kush, conquer bits of India (then unknown to the Greeks) and was only stopped from going further when his army said &quot;it&#x27;s been long enough, can we go home?&quot; He died 3 years later, at age 32. Obviously, he is very much an outlier.