Adam Clarke on 1 Timothy 5:1

Rebuke not an elder - That is, an elderly person; for the word πρεσβυτερος is here taken in its natural sense, and signifies one advanced in years. At 1Tim 5:17, it is taken in what may be termed its ecclesiastical meaning, and signifies, an officer in the Church, what we commonly call a presbyter or bishop; for sometimes these terms were confounded. There are but few cases in which it at all becomes a young man to reprove an old man, and especially one who is a father in the Church. If such a one does wrong, or gets out of the way, he should be entreated as a father, with great caution and respect. To this at least his age entitles him. The word επιπληξῃς signifies, do not smite; i.e. do not treat them harshly, nor with magisterial austerity.

The younger men as brethren - Showing humility, and arrogating nothing to thyself on account of thy office. Feel for them as thou oughtest to feel for thy own brethren.