Dhīra means sober. Just like... The exact translation is "gentleman," dhīra. Those who are not gentlemen, uncultured, uneducated, rascal, they cannot understand. Otherwise where is the difficulty?
How plainly, how easily explained that kaumāraṁ yauvanaṁ jarā. There are three stages, kaumāram. Up to fifteenth year, it is called kaumāra. And then from sixteenth year, it begins youthful life up to fortieth year. Then after forty, one becomes jarā, old man. Primarily old man and later on. Say, forty to fifty, primarily old man, and after fifty, he is old man. Therefore it is advised pañcāś ordhvaṁ vanaṁ vrajet. Pañcāś means fifty. Ūrdhvam, fifty-one. And rest of the days, maybe one hundred years, but that is not possible nowadays. Maybe seventy, eighty, utmost. Somebody lives ninety, ninety-five. Hundred years, although the limit, nowadays nobody lives. So those who are dhīra, gentlemen, sober-headed, cool-headed, they can understand that "I have changed my body. When I was a boy, up to fifteenth year, I remember how I was playing, how I was jumping. Then I became young man. How I was enjoying my life with friends and families. Now I am old man." "I am" means my body.