What is the title for the oldest hymn in which the author is known and when was it approximately written?

Shepherd of Tender Youth

Words: Attributed to Clement of Alexandria (Titus Flavius Clemens), circa 200; translated from Greek to English by Henry M. Dexter, 1846, alt. This is probably the oldest Christian hymn whose author is known.

Shepherd of tender youth, guiding in love and truth
Through devious ways; Christ our triumphant King,
We come Thy Name to sing and here our children bring
To join Thy praise.

Thou art our holy Lord, O all subduing Word,
Healer of strife. Thou didst Thyself abase
That from sin’s deep disgrace Thou mightest save our race
And give us life.

Thou art the great High Priest; Thou hast prepared the feast
Of holy love; and in our mortal pain,
None calls on Thee in vain; Help Thou dost not disdain,
Help from above.

Ever be Thou our guide, our shepherd and our pride,
Our staff and song; Jesus, Thou Christ of God,
By Thine enduring Word lead us where Thou hast trod,
Make our faith strong.

So now, and till we die, sound we Thy praises high
And joyful sing; infants and the glad throng
Who to Thy church belong, unite to swell the song
To Christ, our King.