Albert Barnes Commentary John 21:16

"He saith to him again a second time, Simon, [son] of John, lovest thou me? He saith unto him, Yea, Lord; thou knowest that I love thee. He saith unto him, Tend my sheep." — John 21:16 (ASV)

Feed my sheep. The word here rendered feed, as has been remarked, is different from the word in the previous verse. It has the sense of governing, caring for, guiding, protecting—the kind of faithful vigilance a shepherd uses to guide his flock, and to provide for their needs and protect them from dangers. It may be implied here that the care needed for the young in the church is to instruct them, and for those in advanced years both to instruct and govern them.

My sheep. This term commonly denotes the church in general, without regard to age (John 10).